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Summary of ATLAS 13 TeV results using the full 2015 and 2016 data-set

This page provides a compact summary of published and preliminary ATLAS physics and performance results on 13 TeV protonproton collision data based on the Run-2 data-set taken in 2015 and 2016. For questions, please, contact the ATLAS physics coordinators. See the central publications page for other results from ATLAS.

This page also provides links to ATLAS Physics Briefings for specific results. These are intended to provide a general introduction to ATLAS physics results for a non-specialist audience.

  GroupFormatShort TitleDate√s (TeV)LLinks
BPHYPaperB^0_s to mumu with 2015+16 13TeV dataFull Title: Study of the rare decays of $B^0_s$ and $B^0$ mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector

Abstract: A study of the decays $B^0_s \to \mu^+\mu^-$ and $B^0 \to \mu^+\mu^-$ has been performed using 26.3 fb$^{-1}$ of 13 TeV LHC proton-proton collision data collected with the ATLAS detector in 2015 and 2016. Since the detector resolution in $\mu^+\mu^-$ invariant mass is comparable to the $B_{s}^{0}-B^0$ mass difference, a single fit determines the signal yields for both decay modes. This results in a measurement of the branching fraction ${\cal B}(B^0_s \to \mu^+\mu^-) = \left( 3.2^{+1.1}_{-1.0} \right) \times 10^{-9}$ and an upper limit ${\cal B}(B^0 \to \mu^+\mu^-) < 4.3 \times 10^{-10}$ at 95% confidence level. The result is combined with the Run 1 ATLAS result, yielding ${\cal B}(B^0_s \to \mu^+\mu^-) = \left( 2.8^{+0.8}_{-0.7} \right) \times 10^{-9}$ and ${\cal B}(B^0 \to \mu^+\mu^-) < 2.1 \times 10^{-10}$ at 95% confidence level. The combined result is consistent with the Standard Model prediction within 2.4 standard deviations.

Keywords: 13 TeV,Rare decays,Branching fraction measurements,Muon pairs,FCNC,2 leptons

07-DEC-181336.2 fb-1Documents | 1812.03017 | Inspire
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EGAMPaperElectron reconstruction and identification in the ATLAS experiment using the 2015 and 2016 dataFull Title: Electron reconstruction and identification in the ATLAS experiment using the 2015 and 2016 LHC proton--proton collision data at $\sqrt{s}$ = 13 TeV

Abstract: Algorithms used for the reconstruction and identification of electrons in the central region of the ATLAS detector at the Large Hadron Collider (LHC) are presented in this paper; these algorithms are used in ATLAS physics analyses that involve electrons in the final state and which are based on the 2015 and 2016 proton-proton collision data produced by the LHC at $\sqrt{s } = 13$ TeV. The performance of the electron reconstruction, identification, isolation, and charge identification algorithms is evaluated in data and in simulated samples using electrons from $Z\rightarrow ee$ and $J/\psi\rightarrow ee$ decays. Typical examples of combinations of electron reconstruction, identification, and isolation operating points used in ATLAS physics analyses are shown.

Keywords: Electron identification,Electron reconstruction,Electron performance

11-FEB-191336 fb-1Documents | 1902.04655 | Inspire
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EGAMPaperElectron and photon energy calibration using 2015-2016 dataFull Title: Electron and photon energy calibration with the ATLAS detector using 2015-2016 LHC proton-proton collision data

Abstract: This paper presents the electron and photon energy calibration obtained with the ATLAS detector using about 36 fb$^{-1}$ of LHC proton-proton collision data recorded at $\sqrt{s}=13$ TeV in 2015 and 2016. The different calibration steps applied to the data and the optimization of the reconstruction of electron and photon energies are discussed. The absolute energy scale is set using a large sample of $Z$ boson decays into electron--positron pairs. The systematic uncertainty in the energy scale calibration varies between 0.03% to 0.2% in most of the detector acceptance for electrons with transverse momentum close to 45 GeV. For electrons with transverse momentum of 10 GeV the typical uncertainty is 0.3% to 0.8% and it varies between 0.25% and 1% for photons with transverse momentum around 60 GeV. Validations of the energy calibration with $J/\psi \rightarrow e^+e^-$ decays and radiative $Z$ boson decays are also presented.

Keywords: 13 TeV,Electromagnetic energy calibration,Photon performance,Electron performance

10-DEC-181336 fb-1Documents | 1812.03848 | Inspire
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EGAMPaperPhoton efficiency measurements with the ATLAS detector using 2015-2016 LHC proton-proton collision dataFull Title: Measurement of the photon identification efficiencies with the ATLAS detector using LHC Run 2 data collected in 2015 and 2016

Abstract: The efficiency of the photon identification criteria in the ATLAS detector is measured using 36.1 fb$^{-1}$ to 36.7 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 13 TeV collected in 2015 and 2016. The efficiencies are measured separately for converted and unconverted isolated photons, in four different pseudorapidity regions, for transverse momenta between 10 GeV and 1.5 TeV. The results from the combination of three data-driven techniques are compared with the predictions from simulation after correcting the variables describing the shape of electromagnetic showers in simulation for the average differences observed relative to data. Data-to-simulation efficiency ratios are determined to account for the small residual efficiency differences. These factors are measured with uncertainties between 0.5% and 5% depending on the photon transverse momentum and pseudorapidity. The impact of the isolation criteria on the photon identification efficiency, and that of additional soft $pp$ interactions, are also discussed. The probability of reconstructing an electron as a photon candidate is measured in data, and compared with the predictions from simulation. The efficiency of the reconstruction of photon conversions is measured using a sample of photon candidates from $Z\to\mu\mu\gamma$ events, exploiting the properties of the ratio of the energies deposited in the first and second longitudinal layers of the ATLAS electromagnetic calorimeter.

Keywords: Photon reconstruction,Photon performance,Photon identification

11-OCT-181336 fb-1Documents | 1810.05087 | Inspire
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EXOTPaperSearch for Excited Leptons 13 TeV 2016   Full Title: Search for excited electrons singly produced in proton-proton collisions at $\sqrt{s } = 13$ TeV with the ATLAS experiment at the LHC

Abstract: A search for excited electrons produced in $pp$ collisions at $\sqrt{s } = 13$ TeV via a contact interaction $q\bar{q} \to ee^*$ is presented. The search uses 36.1 fb$^{-1}$ of data collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider. Decays of the excited electron via a contact interaction into an electron and a pair of quarks ($eq\bar{q}$) are targeted in final states with two electrons and two hadronic jets, and decays via a gauge interaction into a neutrino and a $W$ boson ($\nu W$) are probed in final states with an electron, missing transverse momentum, and a large-radius jet consistent with a hadronically decaying $W$ boson. No significant excess is observed over the expected backgrounds. Upper limits are calculated for the $pp \to ee^* \to eeq\bar{q}$ and $pp \to ee^* \to e\nu W$ production cross sections as a function of the excited electron mass $m_{e^*}$ at 95% confidence level. The limits are translated into lower bounds on the compositeness scale parameter $\Lambda$ of the model as a function of $m_{e^*}$. For $m_{e^*} < 0.5$ TeV, the lower bound for $\Lambda$ is 11 TeV. In the special case of $m_{e^* } = \Lambda$, the values of $m_{e^*} < 4.8$ TeV are excluded. The presented limits on $\Lambda$ are more stringent than those obtained in previous searches.

Keywords: 13 TeV,Compositeness,Contact interactions,BSM resonance,BSM search,2 jets,2 leptons

07-JUN-191336 fb-1Documents | 1906.03204 | Inspire
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EXOTPaperSearch for highly ionising particles/monopoles   Full Title: Search for magnetic monopoles and stable high-electric-charge objects in 13 TeV proton-proton collisions with the ATLAS detector

Abstract: A search for magnetic monopoles and high-electric-charge objects is presented using 34.4 fb$^{-1}$ of 13 TeV $pp$ collision data collected by the ATLAS detector at the LHC during 2015 and 2016. The considered signature is based upon high ionization in the transition radiation tracker of the inner detector associated with a pencil-shape energy deposit in the electromagnetic calorimeter. The data were collected by a dedicated trigger based on the tracker high-threshold hit capability. The results are interpreted in models of Drell-Yan pair production of stable particles with two spin hypotheses (0 and 1/2) and masses ranging from 200 GeV to 4000 GeV. The search improves by approximately a factor of five the constraints on the direct production of magnetic monopoles carrying one or two Dirac magnetic charges and stable objects with electric charge in the range $20\le |z|\le60$ and extends the charge range to $60<|z|\le 100$.

Keywords: 13 TeV,Other new particle searches,Long-lived massive particles,Long-lived massive particle

24-MAY-191336 fb-1Documents | 1905.10130 | Inspire
Briefing | Internal
EXOTPaperPrompt and Displaced Heavy Neutral Lepton Search 2016 13 TeV   Full Title: Search for heavy neutral leptons in decays of $W$ bosons produced in 13 TeV $pp$ collisions using prompt and displaced signatures with the ATLAS detector

Abstract: The problems of neutrino masses, matter-antimatter asymmetry, and dark matter could be successfully addressed by postulating right-handed neutrinos with Majorana masses below the electroweak scale. In this work, leptonic decays of $W$ bosons extracted from 32.9 fb$^{-1}$ to 36.1 fb$^{-1}$ of 13 TeV proton-proton collisions at the LHC are used to search for heavy neutral leptons (HNLs) that are produced through mixing with muon or electron neutrinos. The search is conducted using the ATLAS detector in both prompt and displaced leptonic decay signatures. The prompt signature requires three leptons produced at the interaction point (either $\mu\mu e$ or $e e\mu$) with a veto on same-flavour opposite-charge topologies. The displaced signature comprises a prompt muon from the $W$ boson decay and the requirement of a dilepton vertex (either $\mu\mu$ or $\mu e$) displaced in the transverse plane by $4-300$ mm from the interaction point. The search sets constraints on the HNL mixing to muon and electron neutrinos for HNL masses in the range $4.5-50$ GeV.

Keywords: 13 TeV,Heavy neutrinos,BSM resonance,Displaced vertex,Long-lived massive particles,BSM search,Long-lived massive particle,b-jets,1 jet,>=3 leptons,2 leptons (same charge)

23-MAY-191336 fb-1Documents | 1905.09787 | Inspire
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EXOTPaperSummary of searches for mediator-based dark matter and scalar dark energy modelsFull Title: Constraints on mediator-based dark matter and scalar dark energy models using $\sqrt s = 13$ TeV $pp$ collision data collected by the ATLAS detector

Abstract: Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to 37 fb$^{-1}$ $\sqrt{s}= 13$ TeV $pp$ collision data collected by the ATLAS detector at the LHC during 2015$-$2016 are summarised in this paper. The results of experimental searches in a variety of final states are interpreted in terms of a set of spin-1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators embedded in extended Higgs sector models. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy).

Keywords: 13 TeV,Simplified DM model,Dark sector,BSM reinterpretation,BSM search,Statistical combination,Dark matter,Higgs,Photon,Z,W,Boosted,MET,b-jets,2 jets,1 jet,Photons,2 leptons,0 lepton

03-MAR-191336 fb-1Documents | 1903.01400 | Inspire
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EXOTPaperSearch for top - anti-top resonances in the hadronic final stateFull Title: Search for heavy particles decaying into a top-quark pair in the fully hadronic final state in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for new particles decaying into a pair of top quarks is performed using proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of $\sqrt{s } = $13 TeV corresponding to an integrated luminosity of 36.1 fb$^{-1}$. Events consistent with top-quark pair production and the fully hadronic decay mode of the top quarks are selected by requiring multiple high transverse momentum jets including those containing $b$-hadrons. Two analysis techniques, exploiting dedicated top-quark pair reconstruction in different kinematic regimes, are used to optimize the search sensitivity to new hypothetical particles over a wide mass range. The invariant mass distribution of the two reconstructed top-quark candidates is examined for resonant production of new particles with various spins and decay widths. No significant deviation from the Standard Model prediction is observed and limits are set on the production cross-section times branching fraction for new hypothetical $Z$ bosons, dark-matter mediators, Kaluza-Klein gravitons and Kaluza-Klein gluons. By comparing with the predicted production cross-sections, the $Z$ boson in the topcolor-assisted-technicolor model is excluded for masses up to 3.1$-$3.6 TeV, the dark-matter mediators in a simplified framework are excluded in the mass ranges from 0.8 TeV to 0.9 TeV and from 2.0 TeV to 2.2 TeV, and the Kaluza-Klein gluon is excluded for masses up to 3.4 TeV, depending on the decay widths of the particles.

Keywords: 13 TeV,BSM resonance,BSM search,Top pair,Boosted,All hadronic,>=3 jets,2 jets

26-FEB-191336 fb-1Documents | 1902.10077 | Inspire
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EXOTPaperSearches for 3rd generation LeptoquarksFull Title: Searches for third-generation scalar leptoquarks in $\sqrt{s}$ = 13 TeV pp collisions with the ATLAS detector

Abstract: Limits are set on the pair production of scalar leptoquarks, where all possible decays of the leptoquark into a quark ($t$, $b$) and a lepton ($\tau$, $\nu$) of the third generation are considered. The limits are presented as a function of the leptoquark mass and the branching ratio into charged leptons for up-type ($\mathrm{LQ}_{3}^{u}$ $\rightarrow t \nu / b \tau$) and down-type ($\mathrm{LQ}_{3}^{d}$ $\rightarrow b \nu / t \tau$) leptoquarks. Many results are reinterpretations of previously published ATLAS searches. In all cases, LHC proton-proton collision data at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. Masses below 800 GeV are excluded for both $\mathrm{LQ}_{3}^{u}$ and $\mathrm{LQ}_{3}^{d}$ independently of the branching ratio, with masses below about 1 TeV being excluded for the limiting cases of branching ratios equal to zero or unity.

Keywords: Taus,Leptoquarks,BSM resonance,13 TeV,BSM search,b-jets

21-FEB-191336 fb-1Documents | 1902.08103 | Inspire
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EXOTPaperSearch for displaced hadronic jets in the calorimeterFull Title: Search for long-lived neutral particles in $pp$ collisions at $\sqrt{s}$ = 13 TeV that decay into displaced hadronic jets in the ATLAS calorimeter

Abstract: This paper describes a search for pairs of neutral, long-lived particles decaying in the ATLAS calorimeter. Long-lived particles occur in many extensions to the Standard Model and may elude searches for new promptly decaying particles. The analysis considers neutral, long-lived scalars with masses between 5 GeV and 400 GeV, produced from decays of heavy bosons with masses between 125 GeV and 1000 GeV, where the long-lived scalars decay into Standard Model fermions. The analysis uses either 10.8 fb$^{-1}$ or 33.0 fb$^{-1}$ of data (depending on the trigger) recorded in 2016 at the LHC with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV. No significant excess is observed, and limits are reported on the production cross section times branching ratio as a function of the proper decay length of the long-lived particles.

Keywords: 13 TeV,Other new particle searches,BSM resonance,Exotic Higgs decays,MVA / machine learning,Long-lived massive particles,BSM search,Long-lived massive particle

08-FEB-191336 fb-1Documents | 1902.03094 | Inspire
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EXOTPaperScalar leptoquarks pair search and differential cross-section measurements in dilepton or dimuon + jet eventsFull Title: Searches for scalar leptoquarks and differential cross-section measurements in dilepton-dijet events in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV with the ATLAS experiment

Abstract: Searches for scalar leptoquarks pair-produced in proton-proton collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider are performed by the ATLAS experiment. A data set corresponding to an integrated luminosity of 36.1 fb$^{-1}$ is used. Final states containing two electrons or two muons and two or more jets are studied, as are states with one electron or muon, missing transverse momentum and two or more jets. No statistically significant excess above the Standard Model expectation is observed. The observed and expected lower limits on the leptoquark mass at 95% confidence level extend up to 1.25 TeV for first- and second-generation leptoquarks, as postulated in the minimal Buchm\uller-R\uckl-Wyler model, assuming a branching ratio into a charged lepton and a quark of 50%. In addition, measurements of particle-level fiducial and differential cross sections are presented for the $Z\rightarrow ee$, $Z\rightarrow\mu\mu$ and $t\bar{t}$ processes in several regions related to the search control regions. Predictions from a range of generators are compared with the measurements, and good agreement is seen for many of the observables. However, the predictions for the $Z\rightarrow\ell\ell$ measurements in observables sensitive to jet energies disagree with the data.

Keywords: 2 leptons,13 TeV,Leptoquarks,BSM resonance,MVA / machine learning,BSM search,2 jets

01-FEB-191336.1 fb-1Documents | 1902.00377 | Inspire
HepData | Internal
EXOTPaperSearch for MET plus a single top quarkFull Title: Search for large missing transverse momentum in association with one top-quark in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This paper describes a search for events with one top-quark and large missing transverse momentum in the final state. Data collected during 2015 and 2016 by the ATLAS experiment from 13 TeV proton-proton collisions at the LHC corresponding to an integrated luminosity of 36.1 fb$^{-1}$ are used. Two channels are considered, depending on the leptonic or the hadronic decays of the $W$ boson from the top quark. The obtained results are interpreted in the context of simplified models for dark-matter production and for the single production of a vector-like $T$ quark. In the absence of significant deviations from the Standard Model background expectation, 95% confidence-level upper limits on the corresponding production cross-sections are obtained and these limits are translated into constraints on the parameter space of the models considered.

Keywords: 1 lepton,Other new particle searches,Vector-like quarks,Simplified DM model,BSM search,Dark matter,Single top,Boosted,MET,b-jets,13 TeV,All hadronic

23-DEC-181336 fb-1Documents | 1812.09743 | Inspire
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EXOTPaperSearch for single VLQ to Wb 1 leptonFull Title: Search for single production of vector-like quarks decaying into $Wb$ in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for singly produced vector-like quarks $Q$, where $Q$ can be either a $T$ quark with charge $+2/3$ or a $Y$ quark with charge $-4/3$, is performed in proton-proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of $36.1 \text{fb}^{-1}$, recorded with the ATLAS detector at the LHC in 2015 and 2016. The analysis targets $Q \to Wb$ decays where the $W$ boson decays leptonically. No significant deviation from the expected Standard Model background is observed. Upper limits are set on the $QWb$ coupling strength and the mixing between the Standard Model sector and a singlet $T$ quark or a $Y$ quark from a $(B,Y)$ doublet or a $(T,B,Y)$ triplet, taking into account the interference effects with the Standard Model background. The upper limits set on the mixing angle are as small as $|\sin{\theta_{\text{L}}}|= 0.18$ for a singlet $T$ quark of mass 800 GeV, $|\sin{\theta_{\text{R}}}|= 0.17$ for a $Y$ quark of mass 800 GeV in a $(B,Y)$ doublet model and $|\sin{\theta_{\text{L}}}|= 0.16$ for a $Y$ quark of mass 800 GeV in a $(T,B,Y)$ triplet model. Within a $(B,Y)$ doublet model, the limits set on the mixing parameter $|\sin{\theta_{\text{R}}}|$ are comparable with the exclusion limits from electroweak precision observables in the mass range between about 900 GeV and 1250 GeV.

Keywords: 13 TeV,Vector-like quarks,BSM resonance,BSM search,b-hadron,Boosted,MET,b-jets,>=3 jets,1 lepton

18-DEC-181336 fb-1Documents | 1812.07343 | Inspire
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EXOTPaperMulti-charged particle searchFull Title: Search for heavy long-lived multi-charged particles in proton-proton collisions at $\sqrt{s}$ = 13 TeV using the ATLAS detector

Abstract: A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data with an integrated luminosity of 36.1 fb$^{-1}$ collected in 2015 and 2016 from proton-proton collisions at $\sqrt{s}$ = 13 TeV are examined. Particles producing anomalously high ionization, consistent with long-lived massive particles with electric charges from $|q|= 2e$ to $|q|= 7e$, are searched for. No events are observed, and 95% confidence level cross-section upper limits are interpreted as lower mass limits for a Drell-Yan production model. Multi-charged particles with masses between 50 GeV and 980-1220 GeV are excluded.

Keywords: 13 TeV,Other new particle searches,BSM resonance,Long-lived massive particles,BSM search,Long-lived massive particle,Charged tracks

10-DEC-181336 fb-1Documents | 1812.03673 | Inspire
HepData | Internal
EXOTPaperDisplaced jets in muon systemFull Title: Search for long-lived particles produced in $pp$ collisions at $\sqrt{s}=13$ TeV that decay into displaced hadronic jets in the ATLAS muon spectrometer

Abstract: A search for the decay of neutral, weakly interacting, long-lived particles using data collected by the ATLAS detector at the LHC is presented. The analysis in this paper uses 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s } = 13$ TeV recorded in 2015-2016. The search employs techniques for reconstructing vertices of long-lived particles decaying into jets in the muon spectrometer exploiting a two vertex strategy and a novel technique that requires only one vertex in association with additional activity in the detector that improves the sensitivity for longer lifetimes. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined.

Keywords: 13 TeV,Dark sector,BSM resonance,Exotic Higgs decays,Long-lived massive particles,BSM search,Long-lived massive particle,Charged tracks

18-NOV-181336 fb-1Documents | 1811.07370 | Inspire
HepData | Internal
EXOTPaperZ plus displaced jet in calorimeterFull Title: Search for the production of a long-lived neutral particle decaying within the ATLAS hadronic calorimeter in association with a $Z$ boson from $pp$ collisions at $\sqrt{s } = 13$ TeV

Abstract: This Letter presents a search for the production of a long-lived neutral particle decaying within the ATLAS hadronic calorimeter, in association with a Standard Model $Z$ boson produced via an intermediate scalar boson, where $Z \rightarrow l^+ l^-$ ($l=e,\mu$). The data used were collected by the ATLAS detector during 2015 and 2016 $pp$ collisions with a center-of-mass energy of $\sqrt{s } = 13$ TeV at the Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb$^{-1}$. No significant excess of events is observed above the expected background. Limits on the production cross section of the scalar boson times its decay branching fraction into the long-lived neutral particle are derived as a function of the mass of the intermediate scalar boson, the mass of the long-lived neutral particle, and its $c\tau$ from a few centimeters to one hundred meters. In the case that the intermediate scalar boson is the SM Higgs boson, its decay branching fraction to a long-lived neutral particle with a $c\tau$ approximately between 0.1 m and 7 m is excluded with a 95% confidence level up to 10% for $m_{Z_d}$ between 5 and 15 GeV.

Keywords: 13 TeV,Other new particle searches,Exotic Higgs decays,Long-lived massive particles,BSM search,Long-lived massive particle,Z,1 jet,2 leptons

06-NOV-181336 fb-1Documents | 1811.02542 | Inspire
HepData | Internal
EXOTPaper4 top quark search with 1 or 2 leptonsFull Title: Search for four-top-quark production in the single-lepton and opposite-sign dilepton final states in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for four-top-quark production, $t\bar{t}t\bar{t}$, is presented. It is based on proton-proton collision data with a center-of-mass energy $\sqrt{s } = 13$ TeV collected by the ATLAS detector at the Large Hadron Collider during the year 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. Data are analyzed in both the single-lepton and opposite-sign dilepton channels, characterized by the presence of one or two isolated electrons or muons with high-transverse momentum and multiple jets. A data-driven method is used to estimate the dominant background from top-quark pair production in association with jets. No significant excess above the Standard Model expectation is observed. The result is combined with the previous same-sign dilepton and multilepton searches carried out by ATLAS and an observed (expected) upper limit of 5.3 (2.1) times the four-top-quark Standard Model cross section is obtained at 95% confidence level. Additionally, upper limit on anomalous four-top-quark production cross section is set in the context of an effective field theory model.

Keywords: 13 TeV,BSM resonance,BSM search,>=3 tops,Boosted,MET,b-jets,>=3 jets,2 leptons,1 lepton

06-NOV-181336 fb-1Documents | 1811.02305 | Inspire
Briefing | Internal
EXOTPaperHeavy Neutrino searchFull Title: Search for heavy Majorana or Dirac neutrinos and right-handed $W$ gauge bosons in final states with two charged leptons and two jets at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for heavy right-handed Majorana or Dirac neutrinos $N_R$ and heavy right-handed gauge bosons $W_R$ is performed in events with a pair of energetic electrons or muons, with the same or opposite electric charge, and two energetic jets. The events are selected from $pp$ collision data with an integrated luminosity of 36.1 fb$^{-1}$ collected by the ATLAS detector at $\sqrt{s}$ = 13 TeV. No significant deviations from the Standard Model are observed. The results are interpreted within the theoretical framework of a left-right symmetric model and lower limits are set on masses in the heavy right-handed $W$ boson and neutrino mass plane. The excluded region extends to $m_{W_R } = 4.7$ TeV for both Majorana and Dirac $N_R$ neutrinos.

Keywords: 13 TeV,Heavy neutrinos,BSM search,2 jets,2 leptons (same charge),2 leptons

28-SEP-181336 fb-1Documents | 1809.11105 | Inspire
HepData | Internal
EXOTPaperSearch for events with MET and VBF signatureFull Title: Search for invisible Higgs boson decays in vector boson fusion at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is two energetic jets with $\mathcal{O}(1)$ TeV invariant mass and $\mathcal{O}(100)$ GeV missing transverse momentum. The analysis uses 36.1 fb$^{-1}$ of $pp$ collision data at 13 TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125 GeV particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in Higgs portal models to set limits on the WIMP-nucleon scattering cross section. We also consider invisible decays of additional scalar bosons with masses up to 3 TeV for which the upper limits on the cross section times branching fraction are in the range of $0.3-2.0$ pb.

Keywords: 13 TeV,Other new particle searches,Simplified DM model,Exotic Higgs decays,Higgs to invisible,BSM search,VBF,Dark matter,Higgs,MET,2 jets,0 lepton

18-SEP-181336 fb-1Documents | 1809.06682 | Inspire
Internal
EXOTPaperSearch for a resonance decaying to photon-jetsFull Title: Search for pairs of highly collimated photon-jets in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: Results of a search for the pair production of photon-jets - collimated groupings of photons - in the ATLAS detector at the Large Hadron Collider are reported. Highly collimated photon-jets can arise from the decay of new, highly boosted particles that can decay to multiple photons collimated enough to be identified in the electromagnetic calorimeter as a single, photon-like energy cluster. Data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.7 fb$^{-1}$, were collected in 2015 and 2016. Candidate photon-jet pair production events are selected from those containing two reconstructed photons using a set of identification criteria much less stringent than that typically used for the selection of photons, with additional criteria applied to provide improved sensitivity to photon-jets. Narrow excesses in the reconstructed diphoton mass spectra are searched for. The observed mass spectra are consistent with the Standard Model background expectation. The results are interpreted in the context of a model containing a new, high-mass scalar particle with narrow width, $X$, that decays into pairs of photon-jets via new, light particles, $a$. Upper limits are placed on the cross-section times the product of branching ratios $\sigma \times \mathcal{B}(X \rightarrow aa) \times \mathcal {B}(a \rightarrow \gamma \gamma)^{2}$ for 200 GeV $< m_{X} <$ 2 TeV and for ranges of $ m_a $ from a lower mass of 100 MeV up to between 2 GeV and 10 GeV, depending upon $ m_X $. Upper limits are also placed on $\sigma \times \mathcal{B}(X \rightarrow aa) \times \mathcal {B}(a \rightarrow 3\pi^{0})^{2}$ for the same range of $ m_X $ and for ranges of $ m_a $ from a lower mass of 500 MeV up to between 2 GeV and 10 GeV.

Keywords: 13 TeV,BSM resonance,Exotic Higgs decays,BSM Higgs searches,BSM search,Photons

30-AUG-181336 fb-1Documents | 1808.10515 | Inspire
HepData | Internal
EXOTPaperNon-collimated muon searchFull Title: Search for long-lived particles in final states with displaced dimuon vertices in $pp$ collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector

Abstract: A search is performed for a long-lived particle decaying into a final state that includes a pair of muons of opposite-sign electric charge, using proton-proton collision data collected at $\sqrt{s}= 13$ TeV by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 32.9 fb$^{-1}$. No significant excess over the Standard Model expectation is observed. Limits at 95% confidence level on the lifetime of the long-lived particle are presented in models of new phenomena including gauge-mediated supersymmetry or decay of the Higgs boson, $H$, to a pair of dark photons, $Z_D$. Lifetimes in the range c$\tau$ = 1-2400 cm are excluded, depending on the parameters of the model. In the supersymmetric model, the lightest neutralino is the next-to-lightest supersymmetric particle, with a relatively long lifetime due to its weak coupling to the gravitino, the lightest supersymmetric particle. The lifetime limits are determined for very light gravitino mass and various assumptions for the neutralino mass in the range 300 GeV to 1000 GeV. In the dark photon model, the lifetime limits are interpreted as exclusion contours in the plane of the coupling between the $Z_D$ and the Standard Model $Z$ boson versus the $Z_D$ mass (in the range 20-60 GeV), for various assumptions for the $H\rightarrow Z_D Z_D$ branching fraction.

Keywords: 13 TeV,GGM/GMSB,Long-lived massive particles,BSM search,Long-lived massive particle

09-AUG-181336 fb-1Documents | 1808.03057 | Inspire
Internal
EXOTPaperVV/VH and ll/lv heavy resonance search combinationFull Title: Combination of searches for heavy resonances decaying into bosonic and leptonic final states using 36 fb$^{-1}$ of proton-proton collision data at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: Searches for new heavy resonances decaying into different pairings of $W$, $Z$, or Higgs bosons, as well as directly into leptons, are presented using a data sample corresponding to 36.1fb$^{-1}$ of $pp$ collisions at $\sqrt{s } = 13$ TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting bosonic decay modes in the $qqqq$, $\nu\nu qq$, $\ell\nu qq$, $\ell\ell qq$, $\ell\nu\ell\nu$, $\ell\ell\nu\nu$, $\ell\nu\ell\ell$, $\ell\ell\ell\ell$, $qqbb$, $\nu\nu bb$, $\ell\nu bb$, and $\ell\ell bb$ final states are combined, searching for a narrow-width resonance. Likewise, analyses selecting the leptonic $\ell\nu$ and $\ell\ell$ final states are also combined. These two sets of analyses are then further combined. No significant deviation from the Standard Model predictions is observed. Three benchmark models are tested: a model predicting the existence of a new heavy scalar singlet, a simplified model predicting a heavy vector-boson triplet, and a bulk Randall-Sundrum model with a heavy spin-2 Kaluza-Klein excitation of the graviton. Cross-section limits are set at the 95% confidence level using an asymptotic approximation and are compared with predictions for the benchmark models. These limits are also expressed in terms of constraints on couplings of the heavy vector-boson triplet to quarks, leptons, and the Higgs boson. The data exclude a heavy vector-boson triplet with mass below 5.5 TeV in a weakly coupled scenario and 4.5 TeV in a strongly coupled scenario, as well as a Kaluza-Klein graviton with mass below 2.3 TeV.

Keywords: 0 lepton,Heavy vector triplets,BSM resonance,BSM Higgs searches,BSM reinterpretation,BSM search,Statistical combination,Di-Higgs,VH,Vphoton,ZZ,WZ,WW,Boosted,MET,b-jets,13 TeV,2 jets,1 jet,2 leptons,1 lepton

07-AUG-181336 fb-1Documents | 1808.02380 | Inspire
Briefing | Internal
EXOTPaperVLQ pair search combinationFull Title: Combination of the searches for pair-produced vector-like partners of the third-generation quarks at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A combination of the searches for pair-produced vector-like partners of the top and bottom quarks in various decay channels ($T$$\rightarrow$$Zt/Wb/Ht$, $B$$\rightarrow$$Zb/Wt/Hb$) is performed using 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s } = 13$ TeV with the ATLAS detector at the Large Hadron Collider. The observed data are found to be in good agreement with the Standard Model background prediction in all individual searches. Therefore, combined 95% confidence level upper limits are set on the production cross-section for a range of vector-like quark scenarios, significantly extending the reach of the individual searches. A singlet $T$ is excluded for masses below 1.31 TeV and a singlet $B$ is excluded for masses below 1.22 TeV. Assuming a weak isospin $(T,B)$ doublet, $T$ and $B$ masses below 1.37 TeV are excluded.

Keywords: Vector-like quarks,BSM resonance,BSM reinterpretation,BSM search,Statistical combination,Higgs,Single top,Z,W,b-hadron,Boosted,MET,b-jets,All hadronic,>=3 jets,2 jets,>=3 leptons,2 leptons (same charge),2 leptons,1 lepton,0 lepton,13 TeV

07-AUG-181336 fb-1Documents | 1808.02343 | Inspire
HepData | Briefing | Internal
EXOTPaperVLQ pair production fully hadronic searchFull Title: Search for pair production of heavy vector-like quarks decaying into hadronic final states in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search is presented for the pair production of heavy vector-like quarks, $T\bar T$ or $B\bar B$, that decay into final states with jets and no reconstructed leptons. Jets in the final state are classified using a deep neural network as arising from hadronically decaying $W/Z$ bosons, Higgs bosons, top quarks, or background. The analysis uses data from the ATLAS experiment corresponding to 36.1 fb$^{-1}$ of proton-proton collisions with a center-of-mass energy of $\sqrt{s } = 13$ TeV delivered by the Large Hadron Collider in 2015 and 2016. No significant deviation from the Standard Model expectation is observed. Results are interpreted assuming the vector-like quarks decay into a Standard Model boson and a third-generation-quark, $T\rightarrow Wb,Ht,Zt$ or $B\rightarrow Wt,Hb,Zb$, for a variety of branching ratios. At 95% confidence level, the observed (expected) lower limit on the vector-like $B$-quark mass for a weak-isospin doublet ($B, Y$) is 950 (890) GeV, and the lower limits on the masses for the pure decays $B\rightarrow Hb$ and $T\rightarrow Ht$, where these results are strongest, are 1010 (970) GeV and 1010 (1010) GeV, respectively.

Keywords: 13 TeV,Vector-like quarks,MVA / machine learning,BSM search,Higgs,Single top,Z,W,c-hadron,b-hadron,Boosted,All hadronic

06-AUG-181336 fb-1Documents | 1808.01771 | Inspire
HepData | Internal
EXOTPaperSame-sign dilepton plus b-jet searchFull Title: Search for new phenomena in events with same-charge leptons and $b$-jets in $pp$ collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector

Abstract: A search for new phenomena in events with two same-charge leptons or three leptons and jets identified as originating from $b$-quarks in a data sample of 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}= 13$ TeV recorded by the ATLAS detector at the Large Hadron Collider is reported. No significant excess is found and limits are set on vector-like quark, four-top-quark, and same-sign top-quark pair production. The observed (expected) 95% CL mass limits for a vector-like $T$- and $B$-quark singlet are $m_T > 0.98 (0.99)$ TeV and $m_B > 1.00 (1.01)$ TeV respectively. Limits on the production of the vector-like $T_{5/3}$-quark are also derived considering both pair and single production; in the former case the lower limit on the mass of the $T_{5/3}$-quark is (expected to be) 1.19 (1.21) TeV. The Standard Model four-top-quark production cross-section upper limit is (expected to be) 69 (29) fb. Constraints are also set on exotic four-top-quark production models. Finally, limits are set on same-sign top-quark pair production. The upper limit on $uu \to tt$ production is (expected to be) 89 (59) fb for a mediator mass of 1 TeV, and a dark-matter interpretation is also derived, excluding a mediator of 3 TeV with a dark-sector coupling of 1.0 and a coupling to ordinary matter above 0.31.

Keywords: 2 leptons (same charge),13 TeV,Other new particle searches,Heavy vector triplets,Vector-like quarks,Simplified DM model,Contact interactions,BSM resonance,BSM search,Dark matter,b-jets,>=3 jets,2 jets

31-JUL-181336.1 fb-1Documents | 1807.11883 | Inspire
HepData | Internal
EXOTPaperSearch in the MET plus V hadronic final stateFull Title: Search for dark matter in events with a hadronically decaying vector boson and missing transverse momentum in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for dark matter (DM) particles produced in association with a hadronically decaying vector boson is performed using $pp$ collision data at a centre-of-mass energy of $\sqrt{s}=13$ TeV corresponding to an integrated luminosity of 36.1 fb$^{-1}$, recorded by the ATLAS detector at the Large Hadron Collider. This analysis improves on previous searches for processes with hadronic decays of $W$ and $Z$ bosons in association with large missing transverse momentum (mono-$W/Z$ searches) due to the larger dataset and further optimization of the event selection and signal region definitions. In addition to the mono-$W/Z$ search, the as yet unexplored hypothesis of a new vector boson $Z^\prime$ produced in association with dark matter is considered (mono-$Z^\prime$ search). No significant excess over the Standard Model prediction is observed. The results of the mono-$W/Z$ search are interpreted in terms of limits on invisible Higgs boson decays into dark matter particles, constraints on the parameter space of the simplified vector-mediator model and generic upper limits on the visible cross sections for $W/Z$+DM production. The results of the mono-$Z^\prime$ search are shown in the framework of several simplified-model scenarios involving DM production in association with the $Z^\prime$ boson.

Keywords: 13 TeV,Other new particle searches,Simplified DM model,BSM search,Dark matter,Z,W,Boosted,MET,All hadronic,2 jets,1 jet,0 lepton

30-JUL-181336 fb-1Documents | 1807.11471 | Inspire
HepData | Internal
EXOTPaperSearch for a resonance decaying to a top and a b in the 1 lepton final stateFull Title: Search for vector-boson resonances decaying to a top quark and bottom quark in the lepton plus jets final state in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for new charged massive gauge bosons, $W^\prime$, is performed with the ATLAS detector at the LHC. Data were collected in proton-proton collisions at a centre-of-mass energy of $\sqrt{s } = 13$ TeV and correspond to an integrated luminosity of 36.1 $\textrm{fb}^{-1}$. This analysis searches for $W^\prime$ bosons in the $W^\prime \rightarrow t\bar{b}$ decay channel in final states with an electron or muon plus jets. The search covers resonance masses between 0.5 and 5.0 TeV and considers right-handed $W^\prime$ bosons. No significant deviation from the Standard Model (SM) expectation is observed and upper limits are set on the $W^\prime \rightarrow t\bar{b}$ cross section times branching ratio and the $W^\prime$ boson effective couplings as a function of the $W^\prime$ boson mass. For right-handed $W^\prime$ bosons with coupling to the SM particles equal to the SM weak coupling constant, masses below 3.15 TeV are excluded at the 95% confidence level. This search is also combined with a previously published ATLAS result for $W^\prime \rightarrow t\bar{b}$ in the fully hadronic final state. Using the combined searches, right-handed $W^\prime$ bosons with masses below 3.25 TeV are excluded at the 95% confidence level.

Keywords: 13 TeV,BSM resonance,BSM search,Statistical combination,Single top,W,b-hadron,Boosted,MET,b-jets,2 jets,1 lepton

27-JUL-181336 fb-1Documents | 1807.10473 | Inspire
HepData | Internal
EXOTPaperLFV heavy resonance searchFull Title: Search for lepton-flavor violation in different-flavor, high-mass final states in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search is performed for a heavy particle decaying into different-flavor, dilepton pairs ($e\mu$, $e\tau$ or $\mu\tau$), using 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV collected in 2015-2016 by the ATLAS detector at the Large Hadron Collider. No excesses over the Standard Model predictions are observed. Bayesian lower limits at the 95% credibility level are placed on the mass of a $Z^{\prime}$ boson, the mass of a supersymmetric $\tau$-sneutrino, and on the threshold mass for quantum black-hole production. For the $Z^{\prime}$ and sneutrino models, upper cross-section limits are converted to upper limits on couplings, which are compared with similar limits from low-energy experiments and which are more stringent for the $e\tau$ and $\mu\tau$ modes.

Keywords: 13 TeV,Other new particle searches,BSM resonance,LFV,BSM search,Taus,2 leptons

17-JUL-181336.1 fb-1Documents | 1807.06573 | Inspire
Internal
EXOTPaperVLQ search with opposite-sign leptonsFull Title: Search for pair- and single-production of vector-like quarks in final states with at least one $Z$ boson decaying into a pair of electrons or muons in $pp$ collision data collected with the ATLAS detector at $\sqrt{s } = 13$ TeV

Abstract: A search for vector-like quarks is presented, which targets their decay into a $Z$ boson and a third-generation Standard Model quark. In the case of a vector-like quark $T$ ($B$) with charge $+2/3e$ ($-1/3e$), the decay searched for is $T \rightarrow Zt$ ($B \rightarrow Zb$). Data for this analysis were taken during 2015 and 2016 with the ATLAS detector at the Large Hadron Collider and correspond to 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s } = 13$ TeV. The final state used is characterized by the presence of a $Z$ boson with high transverse momentum, which is reconstructed from a pair of opposite-sign same-flavor leptons, as well as $b$-tagged jets. Pair- and single-production of vector-like quarks are both taken into account and are each searched for using optimized dileptonic exclusive and trileptonic inclusive event selections. In these selections, the high scalar sum of jet transverse momenta, the presence of high-transverse-momentum large-radius jets, as well as - in the case of the single-production selections - the presence of forward jets are used. No significant excess over the background-only hypothesis is found and exclusion limits at 95% confidence level allow masses of vector-like quarks of $m_T > 1030$ GeV ($m_T > 1210$ GeV) and $m_B > 1010$ GeV ($m_B > 1140$ GeV) in the singlet (doublet) model. In the case of 100% branching ratio for $T\rightarrow Zt$ ($B\rightarrow Zb$), the limits are $m_T > 1340$ GeV ($m_B > 1220$ GeV). Limits at 95% confidence level are also set on the coupling to Standard Model quarks for given vector-like quark masses.

Keywords: 13 TeV,Vector-like quarks,BSM search,Higgs,Top pair,Single top,Z,W,b-hadron,Boosted,MET,b-jets,>=3 jets,2 jets,>=3 leptons,2 leptons

27-JUN-181336 fb-1Documents | 1806.10555 | Inspire
HepData | Internal
EXOTPaperVLQ pair production search in the Wt+X final stateFull Title: Search for pair production of heavy vector-like quarks decaying into high-$p_{\rm T}$ $W$ bosons and top quarks in the lepton-plus-jets final state in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search is presented for the pair production of heavy vector-like $B$ quarks, primarily targeting $B$ quark decays into a $W$ boson and a top quark. The search is based on 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s } = 13$ TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton-plus-jets final state, characterised by a high-transverse-momentum isolated electron or muon, large missing transverse momentum, and multiple jets, of which at least one is $b$-tagged. No significant deviation from the Standard Model expectation is observed. The 95% confidence level lower limit on the $B$ mass is 1350 GeV assuming a 100% branching ratio to $Wt$. In the SU(2) singlet scenario, the lower mass limit is 1170 GeV. This search is also sensitive to a heavy vector-like $B$ quark decaying into other final states ($Zb$ and $Hb$) and thus mass limits on $B$ production are set as a function of the decay branching ratios. The 100% branching ratio limits are found to be also applicable to heavy vector-like $X$ production, with charge $+$5/3, that decay into $Wt$.

Keywords: 13 TeV,Vector-like quarks,BSM resonance,MVA / machine learning,BSM search,W,Boosted,MET,b-jets,>=3 jets,1 lepton

05-JUN-181336 fb-1Documents | 1806.01762 | Inspire
HepData | Internal
EXOTPaperResonance search in the WZ to lvll final stateFull Title: Search for resonant $WZ$ production in the fully leptonic final state in proton-proton collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for a heavy resonance decaying into $WZ$ in the fully leptonic channel (electrons and muons) is performed. It is based on proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. No significant excess is observed over the Standard Model predictions and limits are set on the production cross section times branching ratio of a heavy vector particle produced either in quark-antiquark fusion or through vector-boson fusion. Constraints are also obtained on the mass and couplings of a singly charged Higgs boson, in the Georgi-Machacek model, produced through vector-boson fusion.

Keywords: 13 TeV,Other new particle searches,BSM resonance,Charged Higgs searches,BSM Higgs searches,BSM search,WZ,MET,>=3 leptons

05-JUN-181336 fb-1Documents | 1806.01532 | Inspire
HepData | Internal
EXOTPaperSearch for di-b-jet resonancesFull Title: Search for resonances in the mass distribution of jet pairs with one or two jets identified as $b$-jets in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for new resonances decaying into jets containing $b$-hadrons in $pp$ collisions with the ATLAS detector at the LHC is presented in the dijet mass range from 0.57 TeV to 7 TeV. The dataset corresponds to an integrated luminosity of up to 36.1 fb$^{-1}$ collected in 2015 and 2016 at $\sqrt{s } = 13$ TeV. No evidence of a significant excess of events above the smooth background shape is found. Upper cross-section limits and lower limits on the corresponding signal mass parameters for several types of signal hypotheses are provided at 95% CL. In addition, 95% CL upper limits are set on the cross-sections for new processes that would produce Gaussian-shaped signals in the di-$b$-jet mass distributions.

Keywords: 2 jets,13 TeV,BSM resonance,BSM search,b-hadron,b-jets,All hadronic

23-MAY-181336 fb-1Documents | 1805.09299 | Inspire
HepData | Internal
EXOTPaperSearch for a resonance decaying to W/Z/H plus a photon in the hadronic final stateFull Title: Search for heavy resonances decaying to a photon and a hadronically decaying $Z/W/H$ boson in $pp$ collisions at $\sqrt{s}=13$ $\mathrm{!TeV}$ with the ATLAS detector

Abstract: Many extensions of the Standard Model predict new resonances decaying to a $Z$, $W$, or Higgs boson and a photon. This paper presents a search for such resonances produced in $pp$ collisions at $\sqrt{s } = 13$ TeV using a dataset with an integrated luminosity of 36.1 fb$^{-1}$ collected by the ATLAS detector at the Large Hadron Collider. The $Z/W/H$ bosons are identified through their decays to hadrons. The data are found to be consistent with the Standard Model expectation in the entire investigated mass range. Upper limits are set on the production cross section times branching fraction for resonance decays to $Z/W+\gamma$ in the mass range from 1.0 to 6.8 TeV, and for the first time into $H+\gamma$ in the mass range from 1.0 to 3.0 TeV.

Keywords: 13 TeV,Other new particle searches,Heavy vector triplets,BSM resonance,BSM Higgs searches,BSM search,Vphoton,Boosted,b-jets,1 jet

04-MAY-181336 fb-1Documents | 1805.01908 | Inspire
HepData | Briefing | Internal
EXOTPaperSearch for top - anti-top resonances in the 1 lepton plus jets final stateFull Title: Search for heavy particles decaying into top-quark pairs using lepton-plus-jets events in proton--proton collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for new heavy particles that decay into top-quark pairs is performed using data collected from proton--proton collisions at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The integrated luminosity of the data sample is 36.1 fb$^{-1}$. Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay. Jets identified as likely to contain $b$-hadrons are required to reduce the background from other Standard Model processes. The invariant mass spectrum of the candidate top-quark pairs is examined for excesses above the background expectation. No significant deviations from the Standard Model predictions are found. Exclusion limits are set on the production cross-section times branching ratio for hypothetical $Z$ bosons, Kaluza--Kein gluons and Kaluza--Klein gravitons that decay into top-quark pairs.

Keywords: 13 TeV,Strong gravity,BSM resonance,Other top properties,Top properties measurements,BSM search,Top pair,Boosted,MET,b-jets,>=3 jets,2 jets,1 lepton

28-APR-181335 fb-1Documents | 1804.10823 | Inspire
Internal
EXOTPaperLFV Z with hadronic tau searchFull Title: Title: A search for lepton-flavor-violating decays of the $Z$ boson into a $\tau$-lepton and a light lepton with the ATLAS detector

Abstract: Direct searches for lepton flavor violation in decays of the $Z$ boson with the ATLAS detector at the LHC are presented. Decays of the $Z$ boson into an electron or muon and a hadronically decaying $\tau$-lepton are considered. The searches are based on a data sample of proton--proton collisions collected by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb$^{-1}$ at a center-of-mass energy of $\sqrt{s } = 13$ TeV. No significant excess of events above the expected background is observed, and upper limits on the branching ratios of lepton-flavor-violating decays are set at the 95% confidence level: $\mathcal{B} (Z\to e\tau) < 5.8 \times 10^{-5}$ and $\mathcal{B} (Z\to \mu\tau) < 2.4 \times 10^{-5}$. This is the first limit on $\mathcal{B} (Z\to e\tau)$ with ATLAS data. The upper limit on $\mathcal{B} (Z\to \mu\tau)$ is combined with a previous ATLAS result based on 20.3 fb$^{-1}$ of proton--proton collision data at a center-of-mass energy of $\sqrt{s } = 8$ TeV and the combined upper limit at 95% confidence level is $\mathcal{B} (Z\to \mu\tau) < 1.3 \times 10^{-5}$.

Keywords: 13 TeV,BSM resonance,LFV,BSM search,Z,Taus,2 leptons

25-APR-181336 fb-1Documents | 1804.09568 | Inspire
Internal
EXOTPaperSearch for HH to bbbbFull Title: Search for pair production of Higgs bosons in the $b\bar{b}b\bar{b}$ final state using proton-proton collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for Higgs boson pair production in the $b\bar{b}b\bar{b}$ final state is carried out with up to 36.1 $\mathrm{fb}^{-1}$ of LHC proton--proton collision data collected at $\sqrt{s } = 13$ TeV with the ATLAS detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. Two analyses are carried out, each implementing a particular technique for the event reconstruction that targets Higgs bosons reconstructed as pairs of jets or single boosted jets. The resonance mass range covered is 260--3000 GeV. The analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to $b\bar{b}b\bar{b}$ are set in each model. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction.

Keywords: 13 TeV,BSM resonance,BSM Higgs searches,Di-Higgs production,BSM search,Di-Higgs,Boosted,b-jets,All hadronic,>=3 jets,2 jets

17-APR-181336 fb-1Documents | 1804.06174 | Inspire
HepData | Internal
EXOTPaperLow-mass dijet resonance search with trigger-level analysisFull Title: Search for low-mass dijet resonances using trigger-level jets with the ATLAS detector in $pp$ collisions at $\sqrt{s}=13$ TeV

Abstract: Searches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, whose data-collection rates at low transverse momentum are much lower than the rate from Standard Model multijet production. This Letter describes a new search for dijet resonances where this limitation is overcome by recording only the event information calculated by the jet trigger algorithms, thereby allowing much higher event rates with reduced storage needs. The search targets low-mass dijet resonances in the range 450-1800 GeV. The analyzed dataset has an integrated luminosity of up to 29.3 fb$^{-1}$ and was recorded at a center-of-mass energy of 13 TeV. No excesses are found; limits are set on Gaussian-shaped contributions to the dijet mass distribution from new particles and on a model of dark-matter particles with axial-vector couplings to quarks.

Keywords: 13 TeV,BSM resonance,Trigger-level objects,BSM search,All hadronic,2 jets

10-APR-181336 fb-1Documents | 1804.03496 | Inspire
HepData | Briefing | Internal
EXOTPaperA to Zh search in the llbb final state with non-SM h Full Title: Search for a heavy Higgs boson decaying into a $Z$ boson and another heavy Higgs boson in the $\ell\ell bb$ final state in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for a heavy neutral Higgs boson, $A$, decaying into a $Z$ boson and another heavy Higgs boson, $H$, is performed using a data sample corresponding to an integrated luminosity of 36.1 fb$^{-1}$ from proton--proton collisions at $\sqrt{s } = 13$ TeV recorded in 2015 and 2016 by the ATLAS detector at the Large Hadron Collider. The search considers the $Z$ boson decaying to electrons or muons and the $H$ boson into a pair of $b$-quarks. No evidence for the production of an $A$ boson is found. Considering each production process separately, the 95% confidence-level upper limits on the $pp\rightarrow A\rightarrow ZH$ production cross-section times the branching ratio $H\rightarrow bb$ are in the range of 14--830 fb for the gluon--gluon fusion process and 26--570 fb for the $b$-associated process for the mass ranges 130--700 GeV of the $H$ boson and process for the mass ranges 130--700 GeV of the $H$ boson and 230--800 GeV of the $A$ boson. The results are interpreted in the context of the two-Higgs-doublet model.

Keywords: 13 TeV,BSM resonance,Exotic Higgs production,BSM Higgs searches,Higgs to bb,BSM search,Z,b-jets,>=3 jets,2 jets,2 leptons

03-APR-181336 fb-1Documents | 1804.01126 | Inspire
HepData | Internal
EXOTPaperVLQ pair production search in the Ht+X final stateFull Title: Search for pair production of up-type vector-like quarks and for four-top-quark events in final states with multiple $b$-jets with the ATLAS detector

Abstract: A search for pair production of up-type vector-like quarks ($T$) with a significant branching ratio into a top quark and either a Standard Model Higgs boson or a $Z$ boson is presented. The same analysis is also used to search for four-top-quark production in several new physics scenarios. The search is based on a dataset of $pp$ collisions at $\sqrt{s}=13$ TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb$^{-1}$. Data are analysed in the lepton+jets final state, characterised by an isolated electron or muon with high transverse momentum, large missing transverse momentum and multiple jets, as well as the jets+$E_{T}^{miss}$ final state, characterised by multiple jets and large missing transverse momentum. The search exploits the high multiplicity of jets identified as originating from $b$-quarks, and the presence of boosted, hadronically decaying top quarks and Higgs bosons reconstructed as large-radius jets, characteristic of signal events. No significant excess above the Standard Model expectation is observed, and 95% CL upper limits are set on the production cross sections for the different signal processes considered. These cross-section limits are used to derive lower limits on the mass of a vector-like $T$ quark under several branching ratio hypotheses assuming contributions from $T \rightarrow Wb$, $Zt$, $Ht$ decays. The 95% CL observed lower limits on the $T$ quark mass range between 0.99 TeV and 1.43 TeV for all possible values of the branching ratios into the three decay modes considered, significantly extending the reach beyond that of previous searches. Additionally, upper limits on anomalous four-top-quark production are set in the context of an effective field theory model, as well as in an universal extra dimensions model.

Keywords: 13 TeV,Vector-like quarks,BSM resonance,BSM search,Higgs,Top pair,Single top,Boosted,MET,b-jets,>=3 jets,1 lepton,0 lepton

26-MAR-181336 fb-1Documents | 1803.09678 | Inspire
Internal
EXOTPaperH to ZdarkZdark or ZZdark search in the llll final stateFull Title: Search for Higgs boson decays to beyond-the-Standard-Model light bosons in four-lepton events with the ATLAS detector at $\sqrt{s}=13$ TeV

Abstract: A search is conducted for a new beyond-the-Standard-Model boson using events where a Higgs boson with mass 125 GeV decays to four leptons ($\ell = $ $e$ or $\mu$). This decay is presumed to occur via an intermediate state which contains one or two on-shell, promptly decaying bosons: $H\rightarrow ZX/XX \rightarrow 4\ell$, where $X$ is a new vector boson $Z_d$ or pseudoscalar $a$ with mass between 1 and 60 GeV. The search uses $pp$ collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 36.1 fb$^{-1}$ at a centre-of-mass energy $\sqrt{s}=13$ TeV. No significant excess of events above Standard Model background predictions is observed; therefore, upper limits at 95% confidence level are set on model-independent fiducial cross-sections, and on the Higgs boson decay branching ratios to vector and pseudoscalar bosons in two benchmark models.

Keywords: 13 TeV,Dark sector,Exotic Higgs decays,BSM search,Higgs,>=3 leptons

09-FEB-181336 fb-1Documents | 1802.03388 | Inspire
Internal
EXOTPaperBoosted low mass dijet resonances with ISRFull Title: Search for light resonances decaying to boosted quark pairs and produced in association with a photon or a jet in proton--proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This Letter presents a search for new light resonances decaying to pairs of quarks and produced in association with a high-$p_{\textrm{T}}$ photon or jet. The dataset consists of proton-proton collisions with an integrated luminosity of 36.1 fb$^{-1}$ at a centre-of-mass energy of $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. Resonance candidates are identified as massive large-radius jets with substructure consistent with a particle decaying into a quark pair. The mass spectrum of the candidates is examined for local excesses above background. No evidence of a new resonance is observed in the data, which are used to exclude the production of a lepto-phobic axial-vector $Z^\prime$ boson. These results improve upon the limits on light dijet resonances obtained at lower centre-of-mass energies.

Keywords: 13 TeV,BSM resonance,BSM search,ISR,Photon,Boosted,All hadronic,2 jets,Photons

26-JAN-181336 fb-1Documents | 1801.08769 | Inspire
Internal
EXOTPaperSearch for a resonance decaying to a top and a b in the hadronic final stateFull Title: Search for $W \rightarrow tb$ decays in the hadronic final state using $pp$ collisions at $\sqrt{s}=13$ $!TeV$ with the ATLAS detector

Abstract: A search for $W$-boson production in the $W \rightarrow t\bar{b} \rightarrow q\bar{q} b\bar{b}$ decay channel is presented using 36.1 fb$^{-1}$ of 13 TeV proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search is interpreted in terms of both a left-handed and a right-handed chiral $W$ boson within the mass range 1-5 TeV. Identification of the hadronically decaying top quark is performed using jet substructure tagging techniques based on a shower deconstruction algorithm. No significant deviation from the Standard Model prediction is observed and the results are expressed as upper limits on the $W \rightarrow t\bar{b}$ production cross-section times branching ratio as a function of the $W$-boson mass. These limits exclude $W$ bosons with right-handed couplings with masses below 3.0 TeV and $W$ bosons with left-handed couplings with masses below 2.9 TeV, at the 95% confidence level.

Keywords: 2 jets,13 TeV,BSM resonance,BSM search,Single top,b-hadron,Boosted,b-jets,All hadronic,>=3 jets

23-JAN-181336.1 fb-1Documents | 1801.07893 | Inspire
HepData | Internal
EXOTPaperSearch for a resonance in the hadronic tau + MET final stateFull Title: A search for high-mass resonances decaying to $\tau\nu$ in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for high-mass resonances decaying to $\tau\nu$ using proton-proton collisions at $\sqrt{s}$ = 13 TeV produced by the Large Hadron Collider is presented. Only $\tau$-lepton decays with hadrons in the final state are considered. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb$^{-1}$. No statistically significant excess above the Standard Model expectation is observed; model-independent upper limits are set on the visible $\tau\nu$ production cross section. Heavy $W^{\prime}$ bosons with masses less than 3.7 TeV in the Sequential Standard Model and masses less than 2.2-3.8 TeV depending on the coupling in the non-universal G(221) model are excluded at the 95% credibility level.

Keywords: 13 TeV,BSM resonance,BSM search,MET,Taus

22-JAN-181336.1 fb-1Documents | 1801.06992 | Inspire
HepData | Internal
EXOTPaperResonance search in the VH to ll/lv/vv plus bb final stateFull Title: Search for heavy resonances decaying into a $W$ or $Z$ boson and a Higgs boson in final states with leptons and $b$-jets in 36 fb$^{-1}$ of $\sqrt s = 13$ TeV $pp$ collisions with the ATLAS detector

Abstract: A search is conducted for new resonances decaying into a $W$ or $Z$ boson and a 125 GeV Higgs boson in the $\nu\bar{\nu}b\bar{b}$, $\ell^{\pm}{\nu}b\bar{b}$, and $\ell^+\ell^-b\bar{b}$ final states, where $\ell ^{\pm}= e^{\pm}$ or $\mu^{\pm}$, in $pp$ collisions at $\sqrt s = 13$ TeV. The data used correspond to a total integrated luminosity of 36.1 fb$^{-1}$ collected with the ATLAS detector at the Large Hadron Collider during the 2015 and 2016 data-taking periods. The search is conducted by examining the reconstructed invariant or transverse mass distributions of $Wh$ and $Zh$ candidates for evidence of a localised excess in the mass range of 220 GeV up to 5 TeV. No significant excess is observed and the results are interpreted in terms of constraints on the production cross-section times branching fraction of heavy $W^\prime$ and $Z^\prime$ resonances in heavy-vector-triplet models and the CP-odd scalar boson $A$ in two-Higgs-doublet models. Upper limits are placed at the 95 % confidence level and range between $9.0\times 10^{-4}$ pb and $8.1\times 10^{-1}$ pb depending on the model and mass of the resonance.

Keywords: 13 TeV,Heavy vector triplets,BSM resonance,BSM Higgs searches,BSM search,VH,Boosted,MET,b-jets,>=3 jets,2 jets,1 jet,2 leptons,1 lepton,0 lepton

17-DEC-171336.1 fb-1Documents | 1712.06518 | Inspire
HepData | Internal
EXOTPaperMET plus jet searchFull Title: Search for dark matter and other new phenomena in events with an energetic jet and large missing transverse momentum using the ATLAS detector

Abstract: Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses proton--proton collision data corresponding to an integrated luminosity of 36.1 fb${}^{-1}$ at a centre-of-mass energy of 13 TeV collected in 2015 and 2016 with the ATLAS detector at the Large Hadron Collider. Events are required to have at least one jet with a transverse momentum above 250 GeV and no leptons ($e$ or $\mu$). Several signal regions are considered with increasing requirements on the missing transverse momentum above 250 GeV. Good agreement is observed between the number of events in data and Standard Model predictions. The results are translated into exclusion limits in models with pair-produced weakly interacting dark-matter candidates, large extra spatial dimensions, and supersymmetric particles in several compressed scenarios.

Keywords: 13 TeV,Other new particle searches,Strong gravity,Simplified DM model,Stop pair production,Sbottom pair production,Squark pair production,BSM search,ISR,Dark matter,MET,1 jet,0 lepton

09-NOV-171336 fb-1Documents | 1711.03301 | Inspire
HepData | Internal
EXOTPaperSame-sign dilepton resonance search in the multi-lepton final state (including LFV)Full Title: Search for doubly charged Higgs boson production in multi-lepton final states with the ATLAS detector using proton--proton collisions at $\sqrt{s}$ = 13 TeV

Abstract: A search for doubly charged Higgs bosons with pairs of prompt, isolated, highly energetic leptons with the same electric charge is presented. The search uses a proton-proton collision data sample at a centre-of-mass energy of 13 TeV corresponding to 36.1 $\mathrm{fb}^{-1}$ of integrated luminosity recorded in 2015 and 2016 by the ATLAS detector at the LHC. This analysis focuses on the decays $H^{\pm\pm}\rightarrow e^{\pm}e^{\pm}$, $H^{\pm\pm}\rightarrow e^{\pm}\mu^{\pm}$ and $H^{\pm\pm}\rightarrow \mu^{\pm}\mu^{\pm}$, fitting the dilepton mass spectra in several exclusive signal regions. No significant evidence of a signal is observed and corresponding limits on the production cross-section are derived at 95% confidence level. The observed lower limit on the mass of a doubly charged Higgs boson only coupling to left-handed leptons ($e$,$\mu$) varies from 770 GeV to 870 GeV (850 GeV expected) for $B(H^{\pm\pm}\rightarrow \ell^{\pm}\ell^{\pm})$ = 100% and both the expected and observed mass limits are above 450 GeV for $B(H^{\pm\pm}\rightarrow \ell^{\pm}\ell^{\pm})$ = 10% and any combination of partial branching ratios.

Keywords: 13 TeV,BSM resonance,Charged Higgs searches,BSM search,>=3 leptons,2 leptons (same charge)

26-OCT-171336 fb-1Documents | 1710.09748 | Inspire
HepData | Internal
EXOTPaperResonance search in the VV to lvqq final stateFull Title: Search for $WW/WZ$ resonance production in $\ell \nu qq$ final states in $pp$ collisions at $\sqrt{s } = $ 13 TeV with the ATLAS detector

Abstract: A search is conducted for new resonances decaying into a $WW$ or $WZ$ boson pair, where one $W$ boson decays leptonically and the other $W$ or $Z$ boson decays hadronically. It is based on proton--proton collision data with an integrated luminosity of 36.1 fb$^{-1}$ collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV in 2015 and 2016. The search is sensitive to diboson resonance production via vector--boson fusion as well as quark--antiquark annihilation and gluon--gluon fusion mechanisms. No significant excess of events is observed with respect to the Standard Model backgrounds. Several benchmark models are used to interpret the results. Limits on the production cross section are set for a new narrow scalar resonance, a new heavy vector-boson and a spin-2 Kaluza--Klein graviton.

Keywords: 1 lepton,13 TeV,Heavy vector triplets,BSM resonance,BSM search,VBF,WZ,WW,Boosted,MET,b-jets,2 jets,1 jet

19-OCT-171336 fb-1Documents | 1710.07235 | Inspire
HepData | Briefing | Internal
EXOTPaperPhoton + jet resonance searchFull Title: Search for new phenomena in high-mass final states with a photon and a jet from $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search is performed for new phenomena in events having a photon with high transverse momentum and a jet collected in 36.7 fb$^{-1}$ of proton--proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The invariant mass distribution of the leading photon and jet is examined to look for the resonant production of new particles or the presence of new high-mass states beyond the Standard Model. No significant deviation from the background-only hypothesis is observed and cross-section limits for generic Gaussian-shaped resonances are extracted. Excited quarks hypothesized in quark compositeness models and high-mass states predicted in quantum black hole models with extra dimensions are also examined in the analysis. The observed data exclude, at 95% confidence level, the mass range below 5.3 TeV for excited quarks and 7.1 TeV (4.4 TeV) for quantum black holes in the Arkani-Hamed--Dimopoulos--Dvali (Randall--Sundrum) model with six (one) extra dimensions.

Keywords: 13 TeV,Strong gravity,BSM resonance,BSM search,Photon,1 jet,Photons

29-SEP-171336 fb-1Documents | 1709.10440 | Inspire
HepData | Internal
EXOTPaperSearch for a resonance in the XH to qqbb final state where X is a new particleFull Title: A search for resonances decaying into a Higgs boson and a new particle $X$ in the $XH \to qqbb$ final state with the ATLAS detector

Abstract: A search for heavy resonances decaying into a Higgs boson ($H$) and a new particle ($X$) is reported, utilizing 36.1 fb$^{-1}$ of proton--proton collision data at $\sqrt{s } = $ 13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle $X$ is assumed to decay to a pair of light quarks, and the fully hadronic final state $XH \rightarrow q\bar qb\bar b$ is analysed. The search considers the regime of high $XH$ resonance masses, where the $X$ and $H$ bosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of $XH$ mass versus $X$ mass is scanned for evidence of a signal, over a range of $XH$ resonance mass values between 1 TeV and 4 TeV, and for $X$ particles with masses from 50 GeV to 1000 GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of $XH$ and $X$ masses, on the production cross-section of the $XH$ resonance.

Keywords: 13 TeV,BSM resonance,BSM search,Higgs,b-hadron,Boosted,b-jets,All hadronic,2 jets

20-SEP-171336 fb-1Documents | 1709.06783 | Inspire
HepData | Internal
EXOTPaperResonance search in the VV to ll/vv plus qq final stateFull Title: Searches for heavy $ZZ$ and $ZW$ resonances in the $\ell\ell qq$ and $\nu\nu qq$ final states in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This paper reports searches for heavy resonances decaying into $ZZ$ or $ZW$ using data from proton--proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV. The data, corresponding to an integrated luminosity of 36.1 fb$^{-1}$, were recorded with the ATLAS detector in 2015 and 2016 at the Large Hadron Collider. The searches are performed in final states in which one $Z$ boson decays into either a pair of light charged leptons (electrons and muons) or a pair of neutrinos, and the associated $W$ boson or the other $Z$ boson decays hadronically. No evidence of the production of heavy resonances is observed. Upper bounds on the production cross sections of heavy resonances times their decay branching ratios to $ZZ$ or $ZW$ are derived in the mass range 300--5000 GeV within the context of Standard Model extensions with additional Higgs bosons, a heavy vector triplet or warped extra dimensions. Production through gluon--gluon fusion, Drell--Yan or vector-boson fusion are considered, depending on the assumed model.

Keywords: 13 TeV,Heavy vector triplets,BSM resonance,BSM Higgs searches,BSM search,VBF,ZZ,WZ,Boosted,MET,b-jets,2 jets,1 jet,2 leptons,0 lepton

31-AUG-171336 fb-1Documents | 1708.09638 | Inspire
HepData | Briefing | Internal
EXOTPaperResonance search in the VV hadronic final stateFull Title: Search for diboson resonances with boson-tagged jets in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: Narrow resonances decaying into $WW$, $WZ$ or $ZZ$ boson pairs are searched for in 36.7 fb $^{-1}$ of proton--proton collision data at a centre-of-mass energy of $\sqrt{s}=13$ TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The diboson system is reconstructed using pairs of large-radius jets with high transverse momentum and tagged as compatible with the hadronic decay of high-momentum $W$ or $Z$ bosons, using jet mass and substructure properties. The search is sensitive to diboson resonances with masses in the range 1.2-5.0 TeV. No significant excess is observed in any signal region. Exclusion limits are set at the 95% confidence level on the production cross section times branching ratio to dibosons for a range of theories beyond the Standard Model. Lower limits on the mass of new gauge bosons up to 3.5 TeV are set, depending on the assumed model.

Keywords: 13 TeV,BSM resonance,BSM search,ZZ,WZ,WW,Boosted,All hadronic,2 jets

15-AUG-171337 fb-1Documents | 1708.04445 | Inspire
HepData | Briefing | Internal
EXOTPaperResonance search in the VH hadronic final stateFull Title: Search for heavy resonances decaying to a $W$ or $Z$ boson and a Higgs boson in the $q\bar{q}^{(\prime)}b\bar{b}$ final state in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for heavy resonances decaying to a $W$ or $Z$ boson and a Higgs boson in the $q\bar{q}^{(\prime)}b\bar{b}$ final state is described. The search uses 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s } = $ 13 TeV collected by the ATLAS detector at the CERN Large Hadron Collider in 2015 and 2016. The data are in agreement with the Standard Model expectations, with the largest excess found at a resonance mass of 3.0 TeV with a local (global) significance of 3.3 (2.1)~$\sigma$. The results are presented in terms of constraints on a simplified model with a heavy vector triplet. Upper limits are set on the production cross-section times branching ratio for resonances decaying to a $W$ ($Z$) boson and a Higgs boson, itself decaying to $b\bar{b}$, in the mass range between 1.1 and 3.8~\tev; the limits range between 83 and 1.6~fb (77 and 1.1~fb) at 95\% confidence level.

Keywords: 2 jets,13 TeV,Heavy vector triplets,BSM resonance,BSM search,VH,Boosted,b-jets,All hadronic

20-JUL-171336.1 fb-1Documents | 1707.06958 | Inspire
HepData | Internal
EXOTPaperVLQ pair production search in the Wb+X final stateFull Title: Search for pair production of heavy vector-like quarks decaying to high-$p_{T}$ $W$ bosons and $b$ quarks in the lepton-plus-jets final state in $pp$ collisions at $\sqrt{s}$=13 TeV with the ATLAS detector

Abstract: A search is presented for the pair production of heavy vector-like $T$ and $B$ quarks, primarily targeting the $T$ quark decays to a $W$ boson and a $b$-quark. The search is based on $36.1$ fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton-plus-jets final state, including at least one $b$-tagged jet and a large-radius jet identified as originating from the hadronic decay of a high-momentum $W$ boson. No significant deviation from the Standard Model expectation is observed in the reconstructed $T$ mass distribution. The observed 95\% confidence level lower limit on the $T$ mass are 1350 GeV assuming 100\% branching ratio to $Wb$. In the SU(2) singlet scenario, the lower mass limit is 1170 GeV. This search is also sensitive to a heavy vector-like $B$ quark decaying to $Wt$ and other final states. The results are thus reinterpreted to provide a 95\% confidence level lower limit on the $B$ quark mass at 1250 GeV assuming 100\% branching ratio to $Wt$; in the SU(2) singlet scenario, the limit is 1080 GeV. Mass limits on both $T$ and $B$ production are also set as a function of the decay branching ratios. The 100\% branching ratio limits are found to be applicable to heavy vector-like $Y$ and $X$ production that decay to $Wb$ and $Wt$, respectively.

Keywords: 13 TeV,Vector-like quarks,BSM resonance,BSM search,W,Boosted,MET,b-jets,>=3 jets,1 lepton

11-JUL-171336.1 fb-1Documents | 1707.03347 | Inspire
HepData | Internal
EXOTPaperSearch for resonant and non-resonant high-mass phenomena in the dilepton final stateFull Title: Search for new high-mass phenomena in the dilepton final state using 36 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search is conducted for new resonant and non-resonant high-mass phenomena in dielectron and dimuon final states. The search uses 36.1 fb$^{-1}$ of proton-proton collision data, collected at $\sqrt{s}$ = 13 TeV by the ATLAS experiment at the LHC in 2015 and 2016. The dilepton invariant mass is used as the discriminating variable. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% credibility level are set on the cross-section times branching ratio for resonances decaying into dileptons, which are converted to lower limits on the resonance mass, up to 4.1 for the E$_{6}$-motivated Z$_{\chi}$. Lower limits on the $qq \ell\ell$ contact interaction scale are set between 23.5 TeV and 40.1 TeV, depending on the model.

Keywords: 2 leptons,13 TeV,Other new particle searches,Contact interactions,BSM resonance,BSM search

07-JUL-171336.1 fb-1Documents | 1707.02424 | Inspire
HepData | Internal
EXOTPaperMET + H search with H to bbFull Title: Search for Dark Matter Produced in Association with a Higgs Boson Decaying to $b\bar b$ using 36 fb$^{-1}$ of $pp$ collisions at $\sqrt s=13$ TeV with the ATLAS Detector

Abstract: Several extensions of the Standard Model predict associated production of dark-matter particles with a Higgs boson. Such processes are searched for in final states with missing transverse momentum and a Higgs boson decaying to a $b\bar b$ pair with the ATLAS detector using 36.1 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of 13 TeV at the LHC. The observed data are in agreement with the Standard Model predictions and limits are placed on the associated production of dark-matter particles and a Higgs boson.

Keywords: 13 TeV,Simplified DM model,BSM search,Dark matter,Higgs,Boosted,MET,b-jets,2 jets,1 jet

05-JUL-171336.1 fb-1Documents | 1707.01302 | Inspire
HepData | Internal
EXOTPaperSearch for a resonance in the lepton + MET final stateFull Title: Search for a new heavy gauge-boson resonance decaying into a lepton and missing transverse momentum in 36 fb$^{-1}$ of $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS experiment

Abstract: The results of a search for new heavy $W^\prime$ bosons decaying to an electron or muon and a neutrino using proton-proton collision data at a centre-of-mass energy of $\sqrt{s } = 13$ TeV are presented. The dataset was collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb$^{-1}$. As no excess of events above the Standard Model prediction is observed, the results are used to set upper limits on the $W^\prime$ boson cross-section times branching ratio to an electron or muon and a neutrino as a function of the $W^\prime$ mass. Assuming a $W^\prime$ boson with the same couplings as the Standard Model $W$ boson, $W^\prime$ masses below 5.1 TeV are excluded at the 95% confidence level.

Keywords: 13 TeV,Other new particle searches,BSM resonance,BSM search,MET,1 lepton

15-JUN-171336 fb-1Documents | 1706.04786 | Inspire
HepData | Internal
EXOTPaperVLQ pair production search in the Zt+X decay with a 1 lepton plus MET plus jets final stateFull Title: Search for pair production of vector-like top quarks in events with one lepton, jets, and missing transverse momentum in $\sqrt{s } = 13$ TeV pp collisions with the ATLAS detector

Abstract: The results of a search for vector-like top quarks using events with exactly one lepton, at least four jets, and large missing transverse momentum are reported. The search is optimised for pair production of vector-like top quarks in the $Z(\rightarrow \! \! \nu \nu) \, t + X$ decay channel. LHC \textit{pp} collision data at a centre-of-mass energy of $\sqrt{s}=13$ TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 $\mathrm{fb}^{-1}$. No significant excess over the Standard Model expectation is seen and upper limits on the production cross-section of a vector-like $T$ quark pair as a function of the $T$ quark mass are derived. The observed (expected) 95\% CL lower limits on the $T$ mass are 870 GeV (890 GeV) for the weak-isospin singlet model, 1.05 TeV (1.06 TeV) for the weak-isospin doublet model and 1.16 TeV (1.17 TeV) for the pure $Zt$ decay mode. Limits are also set on the mass as a function of the decay branching ratios, excluding large parts of the parameter space for masses below 1 TeV.

Keywords: 13 TeV,Vector-like quarks,BSM resonance,BSM search,Single top,Z,Boosted,MET,>=3 jets,1 lepton

30-MAY-171336.1 fb-1Documents | 1705.10751 | Inspire
HepData | Internal
EXOTPaperMET plus photon searchFull Title: Search for dark matter at $\sqrt{s}=13$ TeV in final states containing an energetic photon and large missing transverse momentum with the ATLAS detector

Abstract: Results of a search for physics beyond the Standard Model in events containing an energetic photon and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. As the number of events observed in data, corresponding to an integrated luminosity of 36.1 $\textrm fb^{-1}$ of proton--proton collisions at a centre-of-mass energy of 13 TeV, is in agreement with the Standard Model expectations, exclusion limits in models where dark-matter candidates are pair-produced are determined. For dark-matter production via an axial-vector or a vector mediator in the s-channel, this search excludes mediator masses below 750--1200 GeV for dark-matter candidate masses below 230--480 GeV at 95% confidence level, depending on the couplings. In an effective theory of dark-matter production, the limits restrict the value of the suppression scale $M_{*}$ to be above 790 GeV at 95% confidence level. A limit is also reported on the production of a high-mass scalar resonance by processes beyond the Standard Model, in which the resonance decays to $Z\gamma$ and the Z boson subsequently decays into neutrinos.

Keywords: 0 lepton,13 TeV,Other new particle searches,Simplified DM model,BSM resonance,BSM search,Dark matter,Vphoton,Photon,MET,Photons

12-APR-171336.1 fb-1Documents | 1704.03848 | Inspire
HepData | Internal
EXOTPaperSearch for resonant and non-resonant high-mass phenomena in the dijet final stateFull Title: Search for new phenomena in dijet events using 37 $fb^{-1}$ of $pp$ collision data collected at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: Dijet events are studied in the proton--proton collision dataset recorded at $\sqrt{s}=13$ TeV with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to integrated luminosities of 3.5 $fb^{-1}$ and 33.5 $fb^{-1}$ respectively. Invariant mass and angular distributions are compared to background predictions and no significant deviation is observed. For resonance searches, a new method for fitting the background component of the invariant mass distribution is employed. The dataset is then used to set upper limits at a 95% confidence level on a range of new physics scenarios. Excited quarks with masses below 6.0 TeV are excluded, and limits are set on quantum black holes, heavy W bosons, W* bosons, and a range of masses and couplings in a Z dark matter mediator model. Model-independent limits on signals with a Gaussian shape are also set, using a new approach allowing factorization of physics and detector effects. From the angular distributions, a scale of new physics in contact interaction models is excluded for scenarios with either constructive or destructive interference. These results represent a substantial improvement over those obtained previously with lower integrated luminosity.

Keywords: 13 TeV,Compositeness,Strong gravity,Contact interactions,BSM resonance,BSM search,All hadronic,2 jets

27-MAR-171336 fb-1Documents | 1703.09127 | Inspire
HepData | Internal
FTAGConference noteb-tagging calibration in W+c events with 13 TeV dataFull Title: Calibration of the $b$-tagging efficiency on charm jets using a sample of W+$c$ events with 2015 ATLAS data

Abstract: The identification of jets containing $b$-hadrons ($b$-jets) is of fundamental importance for many physics analyses performed by the ATLAS experiment. The measurement of the probability to mistakenly identify a jet containing $c$-hadrons ($c$-jet) as a $b$-jet, referred to as the $c$-jet tagging efficiency, is presented. The analysis is performed using a sample of $c$-jets produced in association with a $W$ boson, extracted from $pp$ collisions recorded at $\sqrt{s}$ = 13 TeV during 2015 and 2016, corresponding to an integrated luminosity of approximately 36 $fb^{-1}$. The $W$ boson is identified by an isolated electron and missing transverse energy from the neutrino, and the $c$-jet is identified by a muon stemming from a semileptonic $c$-hadron decay. Data-to-simulation scale factors for the $c$-jet tagging efficiency are computed for calorimeter jets reconstructed using the anti-$k_t$ algorithm with a radius parameter of 0.4. Results are presented for the 60\%, 70\%, 77\% and 85\% efficiency working points of the MV2c10 $b$-jet identification algorithm, integrated and as a function of jet transverse momentum. The results of the measurement performed on $W$+$c$ events are combined with the results of a measurement performed on $t\bar{t}$ events in order to reduce the total uncertainty.

Keywords: 13 TeV,Flavour tagging calibration,b-tag performance,MVA / machine learning,W,c-jets

18-DEC-181336 fb-1Documents | Internal
FTAGConference noteb-tagging efficiency in ttbar semi-leptonic events at 13 TeVFull Title: Calibration of the ATLAS b-tagging algorithm in ttbar semi-leptonic events at 13 TeV

Abstract: The calibration of the ATLAS $b$-tagging algorithm in environments characterised by large jet multiplicity is presented. The calibration uses reconstructed $t\bar{t}$ candidate events collected by the ATLAS detector in proton-proton collisions at $13\,$TeV, with a final state containing one charged lepton, missing transverse momentum and at least four jets. The $b$-tagging efficiencies are measured as a function of the transverse momentum and the pseudo-rapidity of the jets. The results for the data-to-simulation scale factors are presented in an extended tranverse momentum region compared to $b$-tagging calibrations based on dileptonic $t\bar{t}$ events.

Keywords: 13 TeV,Flavour tagging calibration,b-tag performance,MVA / machine learning,Top pair

27-JUL-181336 fb-1Documents | Internal
FTAGConference noteMeasurement of the Jet Vertex Charge algorithm performance for b-jetsFull Title: Measurement of the Jet Vertex Charge algorithm performance for b-jets

Abstract: The Jet Vertex Charge algorithm, developed recently within the ATLAS collaboration, discriminates between jets resulting from the hadronisation of a bottom quark or bottom antiquark. This note describes a measurement of the performance of the algorithm and the extraction of data-to-simulation scale factors, made using $b$-tagged jets in candidate single lepton $t\bar{t}$ events. The data sample was collected by the ATLAS detector at the LHC using $pp$ collisions at $\sqrt{s}$ = 13 TeV in 2015 and 2016 and corresponds to a total integrated luminosity of 36.1 fb$^{-1}$ . Overall, good agreement is found between data and the simulation.

Keywords: 13 TeV,Flavour tagging calibration,Top pair,b-hadron,b-jets

08-JUN-181336 fb-1Documents | Internal
FTAGPaperMeasurement of the b-jet identification efficiency at run-2 using ttbar eventsFull Title: Measurements of $b$-jet tagging efficiency with the ATLAS detector using $t\bar{t}$ events at $\sqrt{s}=13$ TeV

Abstract: The efficiency to identify jets containing $b$-hadrons ($b$-jets) is measured using a high purity sample of dileptonic top quark--antiquark pairs ($t\bar{t}$) selected from the 36.1 fb$^{-1}$ of data collected by the ATLAS detector in 2015 and 2016 from proton--proton collisions produced by the Large Hadron Collider at a centre-of-mass energy $\sqrt{s}=13$ TeV. Two methods are used to extract the efficiency from $t\bar{t}$ events, a combinatorial likelihood approach and a tag-and-probe method. A boosted decision tree, not using $b$-tagging information, is used to select events in which two $b$-jets are present, which reduces the dominant uncertainty in the modelling of the flavour of the jets. The efficiency is extracted for jets in a transverse momentum range from 20 to 300 GeV, with data-to-simulation scale factors calculated by comparing the efficiency measured using collision data to that predicted by the simulation. The two methods give compatible results, and achieve a similar level of precision, measuring data-to-simulation scale factors close to unity with uncertainties ranging from 2% to 12% depending on the jet transverse momentum.

Keywords: 13 TeV,Flavour tagging calibration,b-tag performance,MVA / machine learning,Top pair,c-hadron,b-hadron,b-jets

04-MAY-181336 fb-1Documents | 1805.01845 | Inspire
Internal
FTAGConference noteb-tagging mistag calibration in 13 TeV dataFull Title: Calibration of light-flavour jet b-tagging rates on ATLAS data at sqrt(s) = 13 TeV

Abstract: The identification of jets containing $b$-hadrons is important for the physics programme of the ATLAS experiment at the Large Hadron Collider. Two evaluations of the misidentification rate of light-flavour jets for the $b$-tagging algorithm MV2c10, used in the LHC Run 2 ATLAS analyses, are described. The evaluations are performed in various ranges of jet transverse momenta and pseudorapidities with proton-proton collision data collected at a centre-of-mass energy of ${\sqrt{s } = 13}$~TeV during the years 2015 and 2016. The first evaluation is based on a data sample enriched in light-flavour jets thanks to the application of a dedicated algorithm with much reduced capabilities in tagging $b$-jets and similar performance in mistagging light-flavour jets when compared to the standard $b$-tagging algorithm. The second evaluation is based on a bottom-up approach where the underlying tracking variables in the simulation are adjusted to match performance observed in data; the $b$-tagging algorithm is then re-evaluated to assess the change in the light-flavour jet mistagging probability. The results of both methods are in good agreement and are used to calibrate the mistagging rate predicted by the nominal ATLAS simulation. Calibration factors are in the range of about 1.5 to 3 with uncertainties up to 50%.

Keywords: 13 TeV,Flavour tagging calibration,b-tag performance,MVA / machine learning

20-APR-181336 fb-1Documents | Internal
FTAGConference noteb-tagging charm efficiency from ttbar events at 13 TeVFull Title: Measurement of c-jet tagging efficiency in ttbar events using a likelihood approach

Abstract: A new technique is presented to measure the rate at which charm jets are tagged as $b$-jets based on a data sample of single lepton $t\bar{t}$ events, where one of the $W$-bosons decays leptonically and the other decays to a $c$- and $s$-quark, or other quark pair combinations. The data sample was collected by the ATLAS detector at $\sqrt{s } = 13$ TeV in 2015 and 2016 and corresponds to an integrated luminosity of 36 fb$^{-1}$. A kinematic likelihood technique is used to assign jets to the corresponding $t\bar{t}$ decay products. A likelihood fit is used to extract the $c$-jet tagging efficiency from the pair of jets associated to $W$-boson decays. This new technique is used to calibrate the ATLAS MV2c10 $b$-tagging algorithm.

Keywords: 13 TeV,Flavour tagging calibration,b-tag performance,MVA / machine learning,Top pair,c-jets

02-MAR-181336 fb-1Documents | Internal
HDBSPaperCombination h(125)h(125)   Full Title: Combination of searches for Higgs boson pairs in $pp$ collisions at $\sqrt{s } = $13 TeV with the ATLAS detector

Abstract: This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy $\sqrt{s } = 13$ TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the $bbbb$, $bbWW$, $bb\tau\tau$, $WWWW$, $bb\gamma \gamma$ and $WW\gamma\gamma$ final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. The combined observed limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 times the predicted Standard Model cross-section. Limits are also set on the ratio ($\kappa_{\lambda}$) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level to $-5.0 < \kappa_{\lambda} <12.0$. In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model.

Keywords: Higgs,13 TeV,Di-Higgs production,Higgs to tautau,Higgs to bb,Higgs to WW,Higgs to 2 photons,Statistical combination,Di-Higgs

05-JUN-191336.1 fb-1Documents | 1906.02025 | Inspire
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HIGGConference noteSearch BSM H(125)->tau l (l=e,mu) lepton flavor violating decayFull Title: Searches for lepton-flavour-violating decays of the Higgs boson in $\sqrt{s}=13$ TeV pp collisions with the ATLAS detector

Abstract: This note presents direct searches for lepton flavour violation in Higgs boson decays, $H\rightarrow e\tau$ and $H\rightarrow\mu\tau$, performed with the ATLAS detector at the LHC. The searches are based on a data sample of $pp$ collisions at a centre-of-mass energy $\sqrt{s } = 13$ TeV, corresponding to an integrated luminosity of $36.1\,\text{fb}^{-1}$. No significant excesses over the SM predictions are observed and upper limits on the lepton-flavour-violating branching ratios are set. The observed (median expected) 95\% confidence level upper limits are 0.47% ($0.34^{+0.13}_{-0.10}$ %) and 0.28% ($0.37^{+0.14}_{-0.10}$ %) for $H\rightarrow e\tau$ and $H\rightarrow\mu\tau$, respectively.

Keywords: 13 TeV,Exotic Higgs decays,LFV,BSM search,Higgs,Taus,1 lepton

08-MAY-191336.1 fb-1Documents | Internal
HIGGPaperH(125)->invisible combinationFull Title: Combination of searches for invisible Higgs boson decays with the ATLAS experiment

Abstract: Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for $H\to\textrm{invisible}$ decays where $H$ is produced according to the Standard Model via vector boson fusion, $Z(\ell\ell)H$, and $W\!/\!Z(\textrm{had})H$, all performed with the ATLAS detector using 36.1 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt s = 13$ TeV at the LHC. In combination with the results at $\sqrt s = 7$ and 8 TeV, an exclusion limit on the $H\to\textrm{invisible}$ branching ratio of $0.26 (0.17^{+0.07}_{-0.05})$ at 95% confidence level is observed (expected).

Keywords: 13 TeV,Exotic Higgs decays,Higgs to invisible,Statistical combination,MET

10-APR-197, 8, 135 fb-1, 20 fb-1, 36 fb-1Documents | 1904.05105 | Inspire
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HIGGConference noteSearch BSM bH H->bbFull Title: Search for 2HDM Higgs Bosons Produced in Association with b-quarks and Decaying to b-quarks at sqrt(s) = 13 TeV with the ATLAS detector

Abstract: A search for heavy neutral Higgs bosons produced in association with one or two $b$-quarks and decaying to $b$-quark pairs is presented using 27.8 fb$^{-1}$ of $\sqrt{s}=13$~TeV proton--proton collision data recorded by the ATLAS detector at the Large Hadron Collider during 2015 and 2016. No evidence of a signal is found. Upper limits on the heavy neutral Higgs boson production cross-section times its branching ratio to $b\bar{b}$ are set, ranging from 4.0 to 0.6 pb at 95\% confidence level over a Higgs boson mass range of 450 to 1400~GeV. Results are interpreted within the Two Higgs Doublet Model and the Minimal Supersymmetric Standard Model.

Keywords: 13 TeV,BSM Higgs searches,bH production,Higgs to bb,BSM search,b-jets

25-MAR-191327.8 fb-1Documents | Internal
HIGGPaperVH(125), H->WWFull Title: Measurement of the production cross section for a Higgs boson in association with a vector boson in the $H \rightarrow WW^{\ast} \rightarrow \ell\nu\ell\nu$ channel in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A measurement of the Higgs boson production cross sections via associated $WH$ and $ZH$ production using $H \rightarrow WW^{\ast} \rightarrow \ell\nu\ell\nu$ decays, where $\ell$ stands for either an electron or a muon, is presented. Results for combined $WH$ and $ZH$ production are also presented. The analysis uses events produced in proton-proton collisions collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The data correspond to an integrated luminosity of 36.1 fb$ ^{-1}$ recorded at a centre-of-mass energy of 13 TeV. The products of the $H \rightarrow WW^{\ast}$ branching fraction times the $WH$ and $ZH$ cross sections are measured to be $0.67^{+0.31}_{-0.27}$(stat.)$^{+0.18}_{-0.14}$(syst.) pb and $0.54^{+0.31}_{-0.24}$(stat.)$^{+0.15}_{-0.07}$(syst.) pb respectively, in agreement with the Standard Model predictions.

Keywords: >=3 leptons,Simplified template cross-section,Coupling measurements,H(125) measurements,13 TeV,VH production,Higgs to WW,Cross-section measurement,Higgs,VH,WW

24-MAR-191336.1 fb-1Documents | 1903.10052 | Inspire
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HIGGPaperSearch BSM bH with H-> mu muFull Title: Search for scalar resonances decaying into \mu^{+}\mu^{-} in events with and without b-tagged jets produced in proton-proton collisions at \sqrt{s}=13 TeV with the ATLAS detector

Abstract: A search for a narrow scalar resonance decaying into opposite-sign muon pair produced in events with and without b-tagged jets is presented in this paper. The A search for a narrow scalar resonance decaying into an opposite-sign muon pair produced in events with and without b-tagged jets is presented in this paper. The search uses 36.1 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collision data recorded by the ATLAS experiment at the LHC. No significant excess of events above the expected Standard Model background is observed in the investigated mass range of 0.2 to 1.0 TeV. The observed upper limits at 95% confidence level on the cross section times branching ratio for $b$-quark associated production and gluon-gluon fusion are between 1.9 and 41 fb and 1.6 and 44 fb respectively, which is consistent with expectations.

Keywords: 13 TeV,BSM Higgs searches,Higgs to 2 muons,BSM search,b-hadron,b-jets,2 leptons

23-JAN-191336.1 fb-1Documents | 1901.08144 | Inspire
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HIGGPaperSearch BSM H->HH->4W and HH->4WFull Title: Search for Higgs boson pair production in the $WW^{( * )}WW^{( * )}$ decay channel using ATLAS data recorded at $\sqrt{s}=13$ TeV

Abstract: A search for a pair of neutral, scalar bosons with each decaying into two $W$ bosons is presented using 36.1 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. This search uses three production models: non-resonant and resonant Higgs boson pair production and resonant production of a pair of heavy scalar particles. Three final states, classified by the number of leptons, are analysed: two same-sign leptons, three leptons, and four leptons. No significant excess over the expected Standard Model backgrounds is observed. An observed (expected) 95% confidence-level upper limit of 160 (120) times the Standard Model prediction of non-resonant Higgs pair production cross-section is set from a combined analysis of the three final states. Upper limits are set on the production cross-section times branching ratio of a heavy scalar $X$ decaying into a Higgs boson pair in the mass range of 260 GeV $\le m_X \le$ 500 GeV and the observed (expected) limits range from 9.3 (10) pb to 2.8 (2.6) pb. Upper limits are set on the production cross-section times branching ratio of a heavy scalar $X$ decaying into a pair of heavy scalars $S$ for mass ranges of 280 GeV $\le m_X \le$ 340 GeV and 135 GeV $\le m_S \le$ 165 GeV and the observed (expected) limits range from 2.5 (2.5) pb to 0.16 (0.17) pb.

Keywords: 13 TeV,BSM Higgs searches,Di-Higgs production,Higgs to WW,BSM search,Di-Higgs,WW,>=3 leptons,2 leptons

27-NOV-181336 fb-1Documents | 1811.11028 | Inspire
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HIGGPaperH(125) -> tau tauFull Title: Cross-section measurements of the Higgs boson decaying into a pair of tau-leptons in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A measurement of production cross sections of the Higgs boson in proton-proton collisions is presented in the $H\rightarrow\tau\tau$ decay channel. The analysis is performed using $36.1\mathrm{fb}^{-1}$ of data recorded by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy of $\sqrt{s}=13$ TeV. All combinations of leptonic ($\tau \rightarrow l \nu \bar{\nu}$ with $l = e$, $\mu$) and hadronic ($\tau \to$ hadrons $\nu$) $\tau$ decays are considered. The $H\rightarrow\tau\tau$ signal over the expected background from other Standard Model processes is established with an observed (expected) significance of 4.4 (4.1) standard deviations. Combined with results obtained using data taken at 7 and 8 TeV center-of-mass energies, the observed (expected) significance amounts to 6.4 (5.4) standard deviations and constitutes an observation of $H\rightarrow\tau\tau$ decays. Using the data taken at $\sqrt{s}=13$ TeV, the total cross section in the $H\rightarrow\tau\tau$ decay channel is measured to be $3.77^{+0.60}_{-0.59}\mathrm{(stat.)}^{+0.87}_{-0.74}\mathrm{(syst.)}\mathrm{pb}$, for a Higgs boson of mass 125 GeV assuming the relative contributions of its production modes as predicted by the Standard Model. Total cross sections in the $H\rightarrow\tau\tau$ decay channel are determined separately for vector-boson-fusion production and gluon-gluon-fusion production to be $\sigma ^{\mathrm{VBF}}_{H \to \tau \tau } = 0.28 \pm 0.09\mathrm{(stat.)}^{+0.11}_{-0.09}\mathrm{(syst.)}\mathrm{pb}$ and $\sigma ^{gg \mathrm{F}}_{H \to \tau \tau } = 3.1 \pm 1.0\mathrm{(stat.)}^{+1.6}_{-1.3}\mathrm{(syst.)}\mathrm{pb}$, respectively. Similarly, results of a fit are reported in the framework of simplified template cross sections. All measurements are in agreement with Standard Model expectations.

Keywords: 13 TeV,Coupling measurements,H(125) measurements,VBF production,Gluon fusion production,Higgs to tautau,VBF,Gluon fusion,Cross-section measurement,Higgs,Taus

21-NOV-181336.1 fb-1Documents | 1811.08856 | Inspire
HepData | Internal
HIGGPaperSearch BSM H->HH->bb WW and HH->bb WWFull Title: Search for Higgs boson pair production in the $b\bar{b}WW^{*}$ decay mode at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for Higgs boson pair production in the $b\bar{b}WW^\ast$ decay mode is performed in the $b\bar{b}l\nu qq$ final state using 36.1 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. No evidence of events beyond the background expectation is found. Upper limits on the non-resonant $pp\to HH$ production cross section of 10 pb and on the resonant production cross section as a function of the $HH$ invariant mass are obtained. Resonant production limits are set for scalar and spin-2 graviton hypotheses in the mass range 500 to 3000 GeV.

Keywords: 13 TeV,BSM Higgs searches,Di-Higgs production,Higgs to bb,Higgs to WW,BSM search,Di-Higgs,b-jets

12-NOV-181337 fb-1Documents | 1811.04671 | Inspire
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HIGGPaperH(125) -> WW cross-section, couplingsFull Title: Measurements of gluon-gluon fusion and vector-boson fusion Higgs boson production cross-sections in the $H \to WW^{\ast} \to e\nu\mu\nu$ decay channel in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: Higgs boson production cross-sections in proton-proton collisions are measured in the $H \to WW^{\ast} \to e\nu\mu\nu$ decay channel. The proton--proton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. The product of the $H \to WW^{\ast}$ branching fraction times the gluon--gluon fusion and vector-boson fusion cross-sections are measured to be $11.4 ^{+1.2}_{-1.1} (\mathrm{stat.}) ^{+1.8}_{-1.7}(\mathrm{syst.}) \mathrm{pb}$ and $0.50 ^{+0.24}_{-0.22} (\mathrm{stat.}) \pm 0.17(\mathrm{syst.}) \mathrm{pb}$, respectively, in agreement with Standard Model predictions.

Keywords: 13 TeV,Coupling measurements,H(125) measurements,VBF production,Gluon fusion production,Higgs to WW,VBF,Gluon fusion,Cross-section measurement,Higgs,WW,MET,2 leptons

27-AUG-181336.1 fb-1Documents | 1808.09054 | Inspire
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HIGGPaperSearch BSM H+ -> tbFull Title: Search for charged Higgs bosons decaying into top and bottom quarks at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for charged Higgs bosons heavier than the top quark and decaying via $H^+ \to tb$ is presented. The data analysed corresponds to 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s } = 13$ TeV and was recorded with the ATLAS detector at the LHC in 2015 and 2016. The production of a charged Higgs boson in association with a top quark and a bottom quark, $pp \to tb H^+$, is explored in the mass range from $m_H^+ = $ 200 to 2000 GeV using multi-jet final states with one or two electrons or muons. Events are categorised according to the multiplicity of jets and how likely these are to have originated from hadronisation of a bottom quark. Multivariate techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching fraction of a charged Higgs boson as a function of its mass, which range from 2.9 pb at $m_H^+ = $ 200 GeV to 0.070 pb at $m_H^+ = $ 2000 GeV. The results are interpreted in two benchmark scenarios of the Minimal Supersymmetric Standard Model.

Keywords: b-jets,13 TeV,Charged Higgs searches,BSM Higgs searches,BSM search

10-AUG-181336 fb-1Documents | 1808.03599 | Inspire
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HIGGPaperSearch BSM H++ -> W+W+Full Title: Search for doubly charged scalar bosons decaying into same-sign $W$ boson pairs with the ATLAS detector

Abstract: A search for doubly charged scalar bosons decaying into $W$ boson pairs is presented. It uses a data sample from proton-proton collisions corresponding to an integrated luminosity of 36.1 fb$^{-1}$ collected by the ATLAS detector at the LHC at a centre-of-mass energy of 13 TeV in 2015 and 2016. This search is guided by a model that includes an extension of the Higgs sector through a scalar triplet, leading to a rich phenomenology that includes doubly charged scalar bosons $H^{\pm\pm}$. Those bosons are produced in pairs in proton-proton collisions and decay predominantly into electroweak gauge bosons $H^{\pm\pm}\to W^\pm W^\pm$. Experimental signatures with several leptons, missing transverse energy and jets are explored. No significant deviations from the Standard Model predictions are found. The parameter space of the benchmark model is excluded at 95% confidence level for $H^{\pm\pm}$ bosons with masses between 200 and 220 GeV.

Keywords: W,13 TeV,Charged Higgs searches,BSM Higgs searches,WW

05-AUG-181336.1 fb-1Documents | 1808.01899 | Inspire
Internal
HIGGPaperStudy of H(125) off-shell couplings in 4l and llnunuFull Title: Constraints on off-shell Higgs boson production and the Higgs boson total width in $ZZ\to4\ell$ and $ZZ\to2\ell2\nu$ final states with the ATLAS detector

Abstract: A measurement of off-shell Higgs boson production in the $ZZ\to 4\ell$ and $ZZ\to 2\ell2\nu$ decay channels, where $\ell$ stands for either an electron or a muon, is performed using data from proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV. The data were collected by the ATLAS experiment in 2015 and 2016 at the Large Hadron Collider, and they correspond to an integrated luminosity of 36.1 fb$^{-1}$. An observed (expected) upper limit on the off-shell Higgs signal strength, defined as the event yield normalised to the Standard Model prediction, of 3.8 (3.4) is obtained at 95% confidence level (CL). Assuming the ratio of the Higgs boson couplings to the Standard Model predictions is independent of the momentum transfer of the Higgs production mechanism considered in the analysis, a combination with the on-shell signal-strength measurements yields an observed (expected) 95% CL upper limit on the Higgs boson total width of 14.4 (15.2) MeV.

Keywords: 13 TeV,Off-shell Higgs,Gluon fusion production,Higgs to ZZ,Higgs to 4 lepton,Gluon fusion,Higgs,ZZ,MET,>=3 leptons,2 leptons

03-AUG-181336.1 fb-1Documents | 1808.01191 | Inspire
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HIGGPaperSearch BSM H->HH->bb tau tau and HH->bb tau tauFull Title: A search for resonant and non-resonant Higgs boson pair production in the ${b\bar{b}\tau^+\tau^-}$ decay channel in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for resonant and non-resonant pair production of Higgs bosons in the $b\bar{b}\tau^+\tau^-$ final state is presented. The search uses 36.1 fb$^{-1}$ of $pp$ collision data with $\sqrt{s}= 13$ TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. The semileptonic and fully hadronic decays of the $\tau$-lepton pair are considered. No significant excess above the expected background is observed in the data. The cross-section times branching ratio for non-resonant Higgs boson pair production is constrained to be less than 30.9 fb, 12.7 times the Standard Model expectation, at 95% confidence level. The data are also analyzed to probe resonant Higgs boson pair production, constraining a model with an extended Higgs sector based on two doublets and a Randall-Sundrum bulk graviton model. Upper limits are placed on the resonant Higgs boson pair production cross-section times branching ratio, excluding resonances $X$ in the mass range $305~{\rm GeV} < m_X < 402~{\rm GeV}$ in the simplified hMSSM minimal supersymmetric model for $\tan\beta= 2$ and excluding bulk Randall-Sundrum gravitons $G_{\mathrm{KK}}$ in the mass range $325~{\rm GeV} < m_{G_{\mathrm{KK}}} < 885~{\rm GeV}$ for $k/\overline{M}_{\mathrm{Pl} } = 1$.

Keywords: 13 TeV,Di-Higgs production,Higgs to bb,Di-Higgs,Taus,BSM Higgs searches,Higgs to tautau,BSM search,b-jets

01-AUG-181336 fb-1Documents | 1808.00336 | Inspire
HepData | Internal
HIGGPaperSearch BSM H->HH->WW gamma gamma and HH->WW gamma gammaFull Title: Search for Higgs boson pair production in the $\gamma\gamma WW^{*}$ channel using $pp$ collision data recorded at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: Searches for non-resonant and resonant Higgs boson pair production are performed in the $\gamma\gamma WW^{*}$ channel with the final state of $\gamma\gamma\ell\nu jj$ using 36.1 $\mathrm{fb}^{-1}$ of proton-proton collision data recorded at a centre-of-mass energy of $\sqrt{s } = 13$ TeV by the ATLAS detector at the Large Hadron Collider. No significant deviation from the Standard Model prediction is observed. A 95% confidence-level observed upper limit of 7.7 pb is set on the cross section for non-resonant production, while the expected limit is 5.4 pb. A search for a narrow-width resonance $X$ decaying to a pair of Standard Model Higgs bosons $HH$ is performed with the same set of data, and the observed upper limits on $\sigma(pp \rightarrow X) \times B(X \rightarrow HH)$ range between 40.0 pb and 6.1 pb for masses of the resonance between 260 GeV and 500 GeV, while the expected limits range between 17.6 pb and 4.4 pb. When deriving the limits above, the Standard Model branching ratios of the $H \rightarrow \gamma\gamma$ and $H \rightarrow WW^{*}$ are assumed.

Keywords: 13 TeV,BSM Higgs searches,Di-Higgs production,Higgs to WW,Higgs to 2 photons,BSM search,Di-Higgs,Di-photon,WW,MET,Photons,1 lepton

23-JUL-181336 fb-1Documents | 1807.08567 | Inspire
Internal
HIGGPaperVBF H(125) -> bbFull Title: Search for Higgs bosons produced via vector-boson fusion and decaying into bottom quark pairs in $\sqrt{s } = 13$ $\mathrm{!TeV}$ $pp$ collisions with the ATLAS detector

Abstract: A search for the $b\bar b$ decay of the Standard Model Higgs boson produced through vector-boson fusion is presented. Three mutually exclusive channels are considered: two all-hadronic channels and a photon-associated channel. Results are reported from the analysis of up to 30.6 fb$^{-1}$ of $pp$ data at $\sqrt{s } = 13$ $\mathrm{TeV}$ collected with the ATLAS detector at the LHC. The measured signal strength relative to the Standard Model prediction from the combined analysis is $2.5^{+1.4}_{-1.3}$ for inclusive Higgs boson production and $3.0^{+1.7}_{-1.6}$ for vector-boson fusion production only.

Keywords: 13 TeV,H(125) measurements,VBF production,Higgs to bb,VBF,Higgs,Photon,b-jets,Photons

23-JUL-181330.6 fb-1Documents | 1807.08639 | Inspire
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HIGGPaperSearch BSM H+ -> tau nuFull Title: Search for charged Higgs bosons decaying via $H^{\pm} \to \tau^{\pm}\nu_{\tau}$ in the $\tau$+jets and $\tau$+lepton final states with 36 fb$^{-1}$ of $pp$ collision data recorded at $\sqrt{s } = 13$ TeV with the ATLAS experiment

Abstract: Charged Higgs bosons produced either in top-quark decays or in association with a top-quark, subsequently decaying via $H^{\pm} \to \tau^{\pm}\nu_{\tau}$, are searched for in 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV recorded with the ATLAS detector. Depending on whether the top-quark produced together with $H^{\pm}$ decays hadronically or leptonically, the search targets $\tau$+jets and $\tau$+lepton final states, in both cases with a hadronically decaying $\tau$-lepton. No evidence of a charged Higgs boson is found. For the mass range of $m_{H^{\pm}}$ = 90-2000 GeV, upper limits at the 95% confidence level are set on the production cross-section of the charged Higgs boson times the branching fraction $\mathrm{B}(H^{\pm} \to \tau^{\pm}\nu_{\tau})$ in the range 4.2-0.0025 pb. In the mass range 90-160 GeV, assuming the Standard Model cross-section for $t\overline{t}$ production, this corresponds to upper limits between 0.25% and 0.031% for the branching fraction $\mathrm{B}(t\to bH^{\pm}) \times \mathrm{B}(H^{\pm} \to \tau^{\pm}\nu_{\tau})$.

Keywords: 13 TeV,Charged Higgs searches,BSM Higgs searches,BSM search,MET,Taus

20-JUL-181336.1 fb-1Documents | 1807.07915 | Inspire
HepData | Internal
HIGGPaperSearch BSM H->HH->bb gamma gamma and HH->bb gamma gammaFull Title: Search for Higgs boson pair production in the $\gamma\gamma b\bar{b}$ final state with 13 TeV $pp$ collision data collected by the ATLAS experiment

Abstract: A search is performed for resonant and non-resonant Higgs boson pair production in the $\gamma\gamma b\bar{b}$ final state. The data set used corresponds to an integrated luminosity of 36.1 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess relative to the Standard Model expectation is observed. The observed limit on the non-resonant Higgs boson pair cross-section is 0.73 pb at 95% confidence level. This observed limit is equivalent to 22 times the predicted Standard Model cross-section. The Higgs boson self-coupling ($\kappa_\lambda = \lambda_{HHH} / \lambda_{HHH}^{SM}$) is constrained at 95% confidence level to $-8.2 < \kappa_\lambda < 13.2$. For resonant Higgs boson pair production through X $\rightarrow$ HH $\rightarrow$ $\gamma\gamma b\bar{b}$, the limit is presented, using the narrow-width approximation, as a function of $m_X$ in the range 260 GeV $< m_X <$ 1000 GeV. The observed limits range from 1.1 pb to 0.12 pb over this mass range.

Keywords: 13 TeV,BSM Higgs searches,Di-Higgs production,Higgs to bb,Higgs to 2 photons,BSM search,Di-Higgs,Di-photon,b-jets,Photons

13-JUL-181336.1 fb-1Documents | 1807.04873 | Inspire
Internal
HIGGPaperSearch H(125)/Z->J/psi gamma and Upsilon(nS) gammaFull Title: Searches for exclusive Higgs and $Z$ boson decays into $J/\psi\gamma$, $\psi(2S)\gamma$, and $\Upsilon(nS)\gamma$ at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: Searches for the exclusive decays of the Higgs and $Z$ bosons into a $J/\psi$, $\psi(2S)$, or $\Upsilon(nS)$ ($n=1,2,3$) meson and a photon are performed with a $pp$ collision data sample corresponding to an integrated luminosity of 36.1 $fb^{-1}$ collected at $\sqrt{s}=13$ TeV with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above the expected backgrounds, and 95% confidence-level upper limits on the branching fractions of the Higgs boson decays to $J/\psi\gamma$, $\psi(2S)\gamma$, and $\Upsilon(nS)\gamma$ of $3.5\times10^{-4}$, $2.0\times10^{-3}$, and $(4.9,5.9,5.7)\times10^{-4}$, respectively, are obtained assuming Standard Model production. The corresponding 95% confidence-level upper limits for the branching fractions of the $Z$ boson decays are $2.3\times10^{-6}$, $4.5\times10^{-6}$ and $(2.8,1.7,4.8)\times10^{-6}$, respectively.

Keywords: 13 TeV,Exotic Higgs decays,Higgs to meson+photon,Higgs to cc,Higgs to bb,Photons,2 leptons

02-JUL-181336.1 fb-1Documents | 1807.00802 | Inspire
Internal
HIGGPaperSearch BSM H(125)->2a->bb mu muFull Title: Search for Higgs boson decays into a pair of light bosons in the $bb\mu\mu$ final state in $pp$ collision at $\sqrt{s } = $13 TeV with the ATLAS detector

Abstract: A search for decays of the Higgs boson into a pair of new spin-zero particles, $H \to aa$, where the $a$-bosons decay into a $b$-quark pair and muon pair, is presented. The search uses 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% confidence level are placed on the branching ratio $(\sigma_H / \sigma_{SM}) \times B(H\to aa\to bb\mu\mu)$, ranging from $2\times 10^{-4}$ to $10^{-3}$ in the $a$-boson mass range of $20-60$ GeV. Model-independent limits are set on the visible production cross-section times the branching ratio to the $bb\mu\mu$ final state for new physics, $\sigma_{vis}(X) \times B(X\to bb\mu\mu)$, ranging from 0.1 fb to 0.73 fb for $m_{\mu\mu}$ between 18 and 62 GeV.

Keywords: 13 TeV,NMSSM,Exotic Higgs decays,b-jets,2 leptons

02-JUL-181336.1 fb-1Documents | 1807.00539 | Inspire
Internal
HIGGPaperSearch BSM H(125)->2a->4bFull Title: Search for the Higgs boson produced in association with a vector boson and decaying into two spin-zero particles in the $H \rightarrow aa \rightarrow 4b$ channel in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for exotic decays of the Higgs boson into a pair of spin-zero particles, $H \rightarrow aa$, where the $a$-boson decays into $b$-quarks promptly or with a mean proper lifetime $c\tau_a$ up to 6 mm and has a mass in the range of $20-60$ GeV, is presented. The search is performed in events where the Higgs boson is produced in association with a $W$ or $Z$ boson, giving rise to a signature of one or two charged leptons (electrons or muons) and multiple jets from $b$-quark decays. The analysis is based on the dataset of proton-proton collisions at $\sqrt{s } = 13$ TeV recorded in 2015 and 2016 by the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of $36.1$ fb$^{-1}$. No significant excess of events above the Standard Model background prediction is observed, and 95% confidence-level upper limits are derived for the production cross-sections for $pp \rightarrow WH$, $ZH$ and their combination, times the branching ratio of the decay chain $H \rightarrow aa \rightarrow 4b$. For $a$-bosons which decay promptly, the upper limit on the combination of cross-sections for $WH$ and $ZH$ times the branching ratio of $H \rightarrow aa \rightarrow 4b$ ranges from 3.0 pb for $m_a= 20$ GeV to 1.3 pb for $m_a = 60$ GeV, assuming that the ratio of $WH$ to $ZH$ cross-sections follows the Standard Model prediction. For $a$-bosons with longer proper lifetimes, the most stringent limits are 1.8 pb and 0.6 pb, respectively, at $c\tau_a \sim 0.4$ mm.

Keywords: 13 TeV,NMSSM,Exotic Higgs decays,BSM Higgs searches,Displaced vertex,Long-lived massive particles,Long-lived massive particle,b-jets,All hadronic,>=3 jets

19-JUN-181336 fb-1Documents | 1806.07355 | Inspire
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HIGGPaperH(125) mass from H-> gamma gamma and H->ZZ->4lFull Title: Measurement of the Higgs boson mass in the $H\rightarrow ZZ^* \rightarrow 4\ell$ and $H \rightarrow \gamma\gamma$ channels with $\sqrt{s}=13$ TeV $pp$ collisions using the ATLAS detector

Abstract: The mass of the Higgs boson is measured in the $H\rightarrow ZZ^* \rightarrow 4\ell$ and in the $H\rightarrow \gamma\gamma$ decay channels with 36.1 fb$^{-1}$ of proton-proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector in 2015 and 2016. The measured value in the $H\rightarrow ZZ^* \rightarrow 4\ell$ channel is $m_{H}^{ZZ^{*} } = 124.79 \pm 0.37$ GeV, while the measured value in the $H\rightarrow \gamma\gamma$ channel is $m_{H}^{\gamma \gamma } = 124.93 \pm 0.40$ GeV. Combining these results with the ATLAS measurement based on 7 TeV and 8 TeV proton-proton collision data yields a Higgs boson mass of $m_H=124.97 \pm 0.24$ GeV.

Keywords: 13 TeV,ZZ,H(125) measurements,Higgs to ZZ,Higgs to 4 lepton,Higgs to 2 photons,Statistical combination,Mass measurement,Higgs,Di-photon,Photons,>=3 leptons

01-JUN-181336.1 fb-1Documents | 1806.00242 | Inspire
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HIGGPaperH(125) combination cross-sections gamma gamma and 4lFull Title: Combined measurement of differential and total cross sections in the $H \rightarrow \gamma \gamma$ and the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channels at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A combined measurement of differential and inclusive total cross sections of Higgs boson production is performed using 36.1 fb$^{-1}$ of 13 TeV proton-proton collision data produced by the LHC and recorded by the ATLAS detector in 2015 and 2016. Cross sections are obtained from measured $H \rightarrow \gamma \gamma$ and $H \rightarrow ZZ^* \rightarrow 4\ell$ event yields, which are combined taking into account detector efficiencies, resolution, acceptances and branching fractions. The total Higgs boson production cross section is measured to be 57.0$^{+6.0}_{-5.9}$ (stat.) $^{+4.0}_{-3.3}$ (syst.) pb, in agreement with the Standard Model prediction. Differential cross-section measurements are presented for the Higgs boson transverse momentum distribution, Higgs boson rapidity, number of jets produced together with the Higgs boson, and the transverse momentum of the leading jet. The results from the two decay channels are found to be compatible, and their combination agrees with the Standard Model predictions.

Keywords: 13 TeV,H(125) measurements,Gluon fusion production,Higgs to ZZ,Higgs to 4 lepton,Higgs to 2 photons,Statistical combination,Differential measurement,Cross-section measurement,Higgs,Di-photon,ZZ,Photons,>=3 leptons

25-MAY-181336.1 fb-1Documents | 1805.10197 | Inspire
HepData | Internal
HIGGPaperSearch BSM VBF H(125)->2a-> jet jet gamma gammaFull Title: Search for Higgs boson decays into pairs of light (pseudo)scalar particles in the $\gamma\gamma jj$ final state in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This Letter presents a search for exotic decays of the Higgs boson to a pair of new (pseudo)scalar particles, $H\to aa$, with a mass in the range 20--60 GeV, and where one of the $a$ bosons decays into a pair of photons and the other to a pair of gluons. The search is performed in event samples enhanced in vector-boson fusion Higgs boson production by requiring two jets with large invariant mass in addition to the Higgs boson candidate decay products. The analysis is based on the full dataset of $pp$ collisions at $\sqrt{s}= 13$ TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 36.7 fb$^{-1}$. The data are in agreement with the Standard Model predictions and an upper limit at the 95% confidence level is placed on the production cross section times the branching ratio for the decay $H\to aa\to \gamma\gamma gg$. This limit ranges from 3.1 pb to 9.0 pb depending on the mass of the $a$ boson.

Keywords: 13 TeV,NMSSM,Exotic Higgs decays,BSM search,VBF,Higgs,Di-photon,>=3 jets,2 jets,Photons

29-MAR-181336.1 fb-1Documents | 1803.11145 | Inspire
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HIGGPaperSearch VH(125) -> ccFull Title: Search for the Decay of the Higgs Boson to Charm Quarks with the ATLAS Experiment

Abstract: A direct search for the Standard Model Higgs boson decaying to a pair of charm quarks is presented. Associated production of the Higgs and $Z$ bosons, in the decay mode $ZH\rightarrow \ell^+ \ell^- c \bar{c}$ is studied. A dataset with an integrated luminosity of 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS experiment at the LHC is used. The $H\rightarrow c\bar{c}$ signature is identified using charm-tagging algorithms. The observed (expected) upper limit on $\sigma(pp \rightarrow ZH) \times \mathcal{B}(H \rightarrow c\bar{c})$ is 2.7 ($3.9^{+2.1}_{-1.1}$) pb at the 95% confidence level for a Higgs boson mass of 125 GeV, while the Standard Model value is 26 fb.

Keywords: 13 TeV,Higgs to cc,Higgs,VH,Z,c-jets,2 leptons,1 lepton

12-FEB-181336.1 fb-1Documents | 1802.04329 | Inspire
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HIGGPaperH(125) -> gamma gamma fiducial differential cross-sections, STXS, couplingsFull Title: Measurements of Higgs boson properties in the diphoton decay channel with 36 fb$^{-1}$ of $pp$ collision data at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: Properties of the Higgs boson are measured in the two-photon final state using 36 fb$^{-1}$ of proton--proton collision data recorded at $\sqrt{s } = 13$ TeV by the ATLAS experiment at the Large Hadron Collider. Cross-section measurements for the production of a Higgs boson through gluon--gluon fusion, vector-boson fusion, and in association with a vector boson or a top-quark pair are reported. The signal strength, defined as the ratio of the observed to the expected signal yield, is measured for each of these production processes as well as inclusively. The global signal strength measurement of $0.99 \pm 0.14$ improves on the precision of the ATLAS measurement at $\sqrt{s } = 7$ and 8 TeV by a factor of two. Measurements of gluon--gluon fusion and vector-boson fusion productions yield signal strengths compatible with the Standard Model prediction. Measurements of simplified template cross sections, designed to quantify the different Higgs boson production processes in specific regions of phase space, are reported. The cross section for the production of the Higgs boson decaying to two isolated photons in a fiducial region closely matching the experimental selection of the photons is measured to be $55 \pm 10$ fb, which is in good agreement with the Standard Model prediction of $64 \pm 2$ fb. Furthermore, cross sections in fiducial regions enriched in Higgs boson production in vector-boson fusion or in association with large missing transverse momentum, leptons or top-quark pairs are reported. Differential and double-differential measurements are performed for several variables related to the diphoton kinematics as well as the kinematics and multiplicity of the jets produced in association with a Higgs boson. These differential cross sections are sensitive to higher order QCD corrections and properties of the Higgs boson, such as its spin and CP quantum numbers. No significant deviations from a wide array of Standard Model predictions are observed. Finally, the strength and tensor structure of the Higgs boson interactions are investigated using an effective Lagrangian, which introduces additional CP-even and CP-odd interactions. No significant new physics contributions are observed.

Keywords: 13 TeV,Simplified template cross-section,Coupling measurements,H(125) measurements,ttH production,VH production,VBF production,Gluon fusion production,Higgs to 2 photons,EFT,VBF,Gluon fusion,Differential measurement,Cross-section measurement,Higgs,Di-photon,Photons

12-FEB-181336.1 fb-1Documents | 1802.04146 | Inspire
Briefing | Internal
HIGGPaperttH(125) H->bbFull Title: Search for the Standard Model Higgs boson produced in association with top quarks and decaying into a $b\bar{b}$ pair in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for the Standard Model Higgs boson produced in association with a top-quark pair, $t\bar{t}H$, is presented. The analysis uses 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 13 TeV, collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search targets the $H \to b\bar{b}$ decay mode. The selected events contain either one or two electrons or muons from the top-quark decays, and are then categorized according to the number of jets and how likely these are to contain $b$-hadrons. Multivariate techniques are used to discriminate between signal and background events, the latter being dominated by $t\bar{t}$ + jets production. For a Higgs boson mass of 125 GeV, the ratio of the measured $t\bar{t}H$ signal cross-section to the Standard Model expectation is found to be $\mu = 0.84^{+0.64}_{-0.61}$. A value of $\mu$ greater than 2.0 is excluded at 95% confidence level while the expected upper limit is $\mu < 1.2$ in the absence of a $t\bar{t}H$ signal.

Keywords: 13 TeV,Coupling measurements,H(125) measurements,ttH production,Higgs to bb,Higgs,Top pair,b-jets,2 leptons,1 lepton

24-DEC-171336.1 fb-1Documents | 1712.08895 | Inspire
Briefing | Internal
HIGGPaperttH(125) to multilepton final states (WW, ZZ, tau tau) and combinationFull Title: Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector

Abstract: A search for the associated production of the Higgs boson with a top quark pair ($t\bar t H$) is reported. The search is performed in multilepton final states using a dataset corresponding to an integrated luminosity of 36.1 fb$^{-1}$ of proton--proton collision data recorded by the ATLAS experiment at a center-of-mass energy $\sqrt{s } = 13$ TeV at the Large Hadron Collider. Higgs boson decays to $WW^*$, $\tau\tau$, and $ZZ^*$ are targeted. Seven final states, categorized by the number and flavor of charged-lepton candidates, are examined for the presence of the Standard Model Higgs boson with a mass of 125 GeV and a pair of top quarks. An excess of events over the expected background from Standard Model processes is found with an observed significance of 4.1 standard deviations, compared to an expectation of 2.8 standard deviations. The best fit for the $t\bar t H$ production cross section is $\sigma(t\bar t H) = 790^{+230}_{-210}$ fb, in agreement with the Standard Model prediction of $507^{+35}_{-50}$ fb. The combination of this result with other $t\bar t H$ searches from the ATLAS experiment using the Higgs boson decay modes to $b\bar b$, $\gamma\gamma$ and $ZZ^* \to 4\ell$, has an observed significance of 4.2 standard deviations, compared to an expectation of 3.8 standard deviations. This provides evidence for the $t\bar t H$ production mode.

Keywords: 13 TeV,Coupling measurements,H(125) measurements,ttH production,Higgs to tautau,Higgs to WW,Higgs to ZZ,Statistical combination,Higgs,Top pair,ZZ,WW,b-jets,Taus,>=3 leptons,2 leptons (same charge)

24-DEC-171336.1 fb-1Documents | 1712.08891 | Inspire
Briefing | Internal
HIGGPaperSearch BSM H->ZZ->4l and llvvFull Title: Search for heavy $ZZ$ resonances in the $\ell^+\ell^-\ell^+\ell^-$ and $\ell^+\ell^-\nu\bar\nu$ final states using proton proton collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector

Abstract: A search for heavy resonances decaying into a pair of $Z$ bosons leading to $\ell^+\ell^-\ell^+\ell^-$ and $\ell^+\ell^-\nu\bar\nu$ final states, where $\ell$ stands for either an electron or a muon, is presented. The search uses proton proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 36.1 fb$^{-1}$ collected with the ATLAS detector during 2015 and 2016 at the Large Hadron Collider. Different mass ranges for the hypothetical resonances are considered, depending on the final state and model. The different ranges span between 200 GeV and 2000 GeV. The results are interpreted as upper limits on the production cross section of a spin 0 or spin 2 resonance. The upper limits for the spin 0 resonance are translated to exclusion contours in the context of Type I and Type II two-Higgs-doublet models, while those for the spin 2 resonance are used to constrain the Randall Sundrum model with an extra dimension giving rise to spin 2 graviton excitations.

Keywords: 13 TeV,BSM Higgs searches,Higgs to ZZ,Higgs to 4 lepton,MET,>=3 leptons,2 leptons

18-DEC-171336.1 fb-1Documents | 1712.06386 | Inspire
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HIGGPaperSearch H(125)/Z->phi gamma and rho gammaFull Title: Search for exclusive Higgs and $Z$ boson decays to $\phi\gamma$ and $\rho\gamma$ with the ATLAS detector

Abstract: A search for the exclusive decays of the Higgs and $Z$ bosons to a $\phi$ or $\rho$ meson and a photon is performed with a $pp$ collision data sample corresponding to an integrated luminosity of up to 35.6 $fb^{-1}$ collected at $\sqrt{s}=13$ TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to $\phi\gamma$ and $\rho\gamma$ of $4.8\times10^{-4}$ and $8.8\times10^{-4}$, respectively. The corresponding 95% confidence level upper limits for the $Z$ boson decays are $0.9\times10^{-6}$ and $25\times10^{-6}$ for $\phi\gamma$ and $\rho\gamma$, respectively.

Keywords: 13 TeV,Exotic Higgs decays,Higgs to meson+photon,Photons,Charged tracks

07-DEC-171336 fb-1Documents | 1712.02758 | Inspire
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HIGGPaperH(125)->4l STXS and couplingsFull Title: Measurement of the Higgs boson coupling properties in the $H\rightarrow ZZ^{*} \rightarrow 4\ell$ decay channel at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: The coupling properties of the Higgs boson are studied in the four-lepton decay channel using 36.1 fb$^{-1}$ of $pp$ collision data from the LHC at a centre-of-mass energy of 13 TeV collected by the ATLAS detector. Cross sections are measured for the four key production modes in several exclusive regions of the Higgs boson production phase space and are interpreted in terms of coupling modifiers. The inclusive cross section times branching ratio for $H \rightarrow ZZ^*$ decay and for a Higgs boson absolute rapidity below 2.5 is measured to be $1.73^{+0.24}_{-0.23}$(stat.)$^{+0.10}_{-0.08}$(exp.)$\pm 0.04$(th.) pb compared to the Standard Model prediction of $1.34\pm0.09$ pb. In addition, the tensor structure of the Higgs boson couplings is studied using an effective Lagrangian approach for the description of interactions beyond the Standard Model. Constraints are placed on the non-Standard-Model CP-even and CP-odd couplings to $Z$ bosons and on the CP-odd coupling to gluons.

Keywords: >=3 leptons,13 TeV,Simplified template cross-section,Coupling measurements,H(125) measurements,ttH production,VH production,VBF production,Gluon fusion production,Higgs to ZZ,Higgs to 4 lepton,EFT,VBF,Gluon fusion,Cross-section measurement,Higgs,ZZ

06-DEC-171336.1 fb-1Documents | 1712.02304 | Inspire
Briefing | Internal
HIGGPaperSearch BSM H->WW->lvlvFull Title: Search for heavy resonances decaying into $WW$ in the $e\nu\mu\nu$ final state in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for neutral heavy resonances is performed in the $WW\to e\nu\mu\nu$ decay channel using $pp$ collision data corresponding to an integrated luminosity of 36.1 fb$^{-1}$, collected at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. No evidence of such heavy resonances is found. In the search for production via the quark--antiquark annihilation or gluon--gluon fusion process, upper limits on $\sigma_X\times B(X \to WW)$ as a function of the resonance mass are obtained in the mass range between 200 GeV and up to 5 TeV for various benchmark models: a Higgs-like scalar in different width scenarios, a two-Higgs-doublet model, a heavy vector triplet model, and a warped extra dimensions model. In the vector-boson fusion process, constraints are also obtained on these resonances, as well as on a Higgs boson in the Georgi--Machacek model and a heavy tensor particle coupling only to gauge bosons.

Keywords: 13 TeV,BSM resonance,BSM Higgs searches,Higgs to WW,BSM search,WW,MET,2 leptons

03-OCT-171336.1 fb-1Documents | 1710.01123 | Inspire
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HIGGPaperSearch BSM A/H/Z->tautauFull Title: Search for additional heavy neutral Higgs and gauge bosons in the ditau final state produced in 36 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for heavy neutral Higgs bosons and $Z^{\prime}$ bosons is performed using a data sample corresponding to an integrated luminosity of 36.1 fb$^{-1}$ from proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded by the ATLAS detector at the LHC during 2015 and 2016. The heavy resonance is assumed to decay to $\tau^+\tau^-$ with at least one tau lepton decaying to final states with hadrons and a neutrino. The search is performed in the mass range of 0.2-2.25 TeV for Higgs bosons and 0.2-4.0 TeV for $Z^{\prime}$ bosons. The data are in good agreement with the background predicted by the Standard Model. The results are interpreted in benchmark scenarios. In the context of the hMSSM scenario, the data exclude $\tan\beta > 1.0$ for $m_A$ = 0.25 TeV and $\tan\beta > 42$ for $m_A$ = 1.5 TeV at the 95% confidence level. For the Sequential Standard Model, $Z^{\prime}_\mathrm{SSM}$ with $m_{Z^{\prime}} < 2.42$ TeV is excluded at 95% confidence level, while $Z^{\prime}_\mathrm{NU}$ with $m_{Z^{\prime}} < 2.25$ TeV is excluded for the non-universal $G(221)$ model that exhibits enhanced couplings to third-generation fermions.

Keywords: 13 TeV,BSM resonance,BSM Higgs searches,Higgs to tautau,BSM search,Taus

21-SEP-171336 fb-1Documents | 1709.07242 | Inspire
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HIGGPaperSearch ZH(125), H(125)->invisible and Z+METFull Title: Search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a $Z$ boson in $pp$ collisions at $\sqrt{s } = $ 13 TeV with the ATLAS detector

Abstract: A search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a leptonically decaying $Z$ boson in proton--proton collisions at $\sqrt{s } = $ 13 TeVis presented. This search uses 36.1 fb$^{-1}$ of data collected by the ATLAS experiment at the Large Hadron Collider. No significant deviation from the background expectation is observed. Assuming the Standard Model $ZH$ production cross-section, an observed (expected) upper limit of 67% (39%) at the 95% confidence level is set on the branching ratio of invisible decays of the Higgs boson with mass $m_H = $ 125 GeV. The corresponding limits on the production cross-section of the $ZH$ process with the invisible Higgs boson decays are also presented. Furthermore, exclusion limits on the dark matter candidate and mediator masses are reported in the framework of simplified dark matter models.

Keywords: 13 TeV,Simplified DM model,Exotic Higgs decays,Higgs to invisible,Dark matter,Z,MET,2 leptons

31-AUG-171336 fb-1Documents | 1708.09624 | Inspire
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HIGGPaperVH(125), H(125)->bbFull Title: Evidence for the $H \to b\bar{b}$ decay with the ATLAS detector

Abstract: A search for the decay of the Standard Model Higgs boson into a $b\bar{b}$ pair when produced in association with a $W$ or $Z$ boson is performed with the ATLAS detector. The analysed data, corresponding to an integrated luminosity of 36.1 fb$^{-1}$, were collected in proton--proton collisions in Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Final states containing zero, one and two charged leptons (electrons or muons) are considered, targeting the decays $Z\to\nu\nu$, $W\to\ell\nu$ and $Z\to\ell\ell$. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed significance of 3.5 standard deviations, compared to an expectation of 3.0 standard deviations. This excess provides evidence for the Higgs boson decay into $b$-quarks and for its production in association with a vector boson. The combination of this result with that of the Run 1 analysis yields a ratio of the measured signal events to the Standard Model expectation equal to $0.90 \pm 0.18 \rm{(stat.)} ^{+0.21}_{-0.19} \rm{(syst.)}$. Assuming the Standard Model production cross-section, the results are consistent with the value of the Yukawa coupling to $b$-quarks in the Standard Model.

Keywords: 13 TeV,H(125) measurements,VH production,Higgs to bb,Higgs,VH,b-jets,2 leptons,1 lepton,0 lepton

10-AUG-171336.1 fb-1Documents | 1708.03299 | Inspire
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HIGGPaperH(125)->4l fiducial differential cross sectionsFull Title: Measurement of inclusive and differential cross sections in the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channel in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: Inclusive and differential fiducial cross sections of Higgs boson production in proton-proton collisions are measured in the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channel. The proton-proton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. The inclusive fiducial cross section in the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channel is measured to be 3.62 $\pm$ 0.50 (stat) $^{+0.25}_{-0.20}$ (sys) fb, in agreement with the Standard Model prediction of 2.91 $\pm$ 0.13 fb. The cross section is also extrapolated to the total phase space including all Standard Model Higgs boson decays. Several differential fiducial cross sections are measured for observables sensitive to the Higgs boson production and decay, including kinematic distributions of jets produced in association with the Higgs boson. Good agreement is found between data and Standard Model predictions. The results are used to put constraints on anomalous Higgs boson interactions with Standard Model particles, using the pseudo-observable extension to the kappa-framework. Inclusive and differential fiducial cross sections of Higgs boson production in proton-proton collisions are measured in the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channel. The proton-proton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. The inclusive fiducial cross section in the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channel is measured to be 3.62 $\pm$ 0.50 (stat) $^{+0.25}_{-0.20}$ (sys) fb, in agreement with the Standard Model prediction of 2.91 $\pm$ 0.13 fb. The cross section is also extrapolated to the total phase space including all Standard Model Higgs boson decays. Several differential fiducial cross sections are measured for observables sensitive to the Higgs boson production and decay, including kinematic distributions of jets produced in association with the Higgs boson. Good agreement is found between data and Standard Model predictions. The results are used to put constraints on anomalous Higgs boson interactions with Standard Model particles, using the pseudo-observable extension to the kappa-framework.

Keywords: 13 TeV,Pseudo-observables,H(125) measurements,Higgs to ZZ,Higgs to 4 lepton,Differential measurement,Cross-section measurement

09-AUG-171336.1 fb-1Documents | 1708.02810 | Inspire
HepData | Internal
HIGGPaperH(125)->Zgam and search BSM H->ZgamFull Title: Searches for the $Z\gamma$ decay mode of the Higgs boson and for new high-mass resonances in pp collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: This article presents searches for the $Z\gamma$ decay of the Higgs boson and for narrow high-mass resonances decaying to $Z\gamma$, exploiting $Z$ boson decays to pairs of electrons or muons. The data analysis uses 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s } = 13$ TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The data are found to be consistent with the expected Standard Model background. The observed (expected -- assuming Standard Model $pp\to H\to Z\gamma$ production and decay) upper limit on the production cross section times the branching ratio for $pp\to H\to Z\gamma$ is 6.6 (5.2) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125.09 GeV. In addition, upper limits are set on the production cross section times the branching ratio as a function of the mass of a narrow resonance between 250 GeV and 2.4 TeV, assuming spin-0 resonances produced via gluon--gluon fusion, and spin-2 resonances produced via gluon--gluon or quark--antiquark initial states. For high-mass spin-0 resonances, the observed (expected) limits vary between 88 fb (61 fb) and 2.8 fb (2.7 fb) for the mass range from 250 GeV to 2.4 TeV at the 95% confidence level.

Keywords: 13 TeV,Exotic Higgs decays,H(125) measurements,Higgs to Z+photon,Higgs,Vphoton,Z,Photons,2 leptons

01-AUG-171336.1 fb-1Documents | 1708.00212 | Inspire
Briefing | Internal
HIGGPaperSearch BSM H/X->gammagammaFull Title: Search for new phenomena in high-mass diphoton final states using 37 fb$^{-1}$ of proton--proton collisions collected at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: Searches for new phenomena in high-mass diphoton final states with the ATLAS experiment at the LHC are presented. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 36.7 fb$^{-1}$ at a centre-of-mass energy $\sqrt{s}=13$ TeV recorded in 2015 and 2016. Searches are performed for resonances with spin 0, as predicted by theories with an extended Higgs sector, and for resonances with spin 2, using a warped extra-dimension model as a benchmark model, as well as for non-resonant signals, assuming a large extra-dimension scenario. No significant deviation from the Standard Model is observed. Upper limits are placed on the production cross section times branching ratio to two photons as a function of hypothesized signal mass for the two resonance models. In addition, lower limits are set on the ultraviolet cutoff scale in the large extra-dimensions model, depending on the number of extra dimensions and the theoretical formalism used.

Keywords: 13 TeV,Strong gravity,BSM resonance,BSM Higgs searches,Higgs to 2 photons,Di-photon,Photons

13-JUL-171337 fb-1Documents | 1707.04147 | Inspire
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HIGGConference noteCombination H(125)->gammagamma and 4l STXS, couplings and fiducial cross sectionsFull Title: Combined measurements of Higgs boson production and decay in the H->ZZ*->4l and H->gammagamma channels using sqrt(s) = 13 TeV pp collision data collected with the ATLAS experiment

Abstract: Combined measurements of Higgs boson production cross sections and branching fractions are presented using the $H\rightarrow\gamma\gamma$ and $H\rightarrow ZZ^∗\rightarrow4\ell$ decay channels, based on 36.1 fb$^{−1}$ of proton–proton collision data recorded by the ATLAS experiment at the LHC at $\sqrt{s}= $ 13 TeV. Results are presented for the individual production processes of gluon fusion, vector-boson fusion, WH, ZH, and t$\bar{\rm{t}}$H , and for kinematic subdivisions of these processes. The total cross section for $pp \rightarrow H + X$ is determined to be $57.0^{+6.0}_{−5.9}$ (stat.) $^{+4.0}_{−3.3}$ (syst.) pb, consistent with the Standard Model prediction of $55.6^{+2.4}_{−3.4}$ pb. The results are translated into constraints on coefficients of Standard Model couplings. No significant deviations from the expectations are observed.

Keywords: 13 TeV,kappa,Simplified template cross-section,Coupling measurements,H(125) measurements,ttH production,VH production,VBF production,Gluon fusion production,Higgs to 4 lepton,Higgs to 2 photons,VBF,Gluon fusion,Statistical combination,Cross-section measurement,Higgs,Di-photon,ZZ,Photons,>=3 leptons

05-JUL-171336.1 fb-1Documents | Internal
HIGGPaperSearch FCNC t->H(125) q, H(125)->gammagammaFull Title: Search for top quark decays $t \rightarrow qH$, with $H\to\gamma\gamma$, in $\sqrt{s } = 13$ TeV $pp$ collisions using the ATLAS detector

Abstract: This article presents a search for flavour-changing neutral currents in the decay of a top quark into an up-type ($q = c, u$) quark and a Higgs boson, where the Higgs boson decays into two photons. The proton--proton collision data set analysed amounts to 36.1 fb$^{-1}$ at $\sqrt{s } = 13$ TeV collected by the ATLAS experiment at the LHC. Top quark pair events are searched for, where one top quark decays into $qH$ and the other decays into $bW$. Both the hadronic and leptonic decay modes of the $W$ boson are used. No significant excess is observed and an upper limit is set on the $t \rightarrow cH$ branching ratio of $2.2\times 10^{-3}$ at the 95% confidence level, while the expected limit in the absence of signal is $1.6 \times 10^{-3}$. The corresponding limit on the $tcH$ coupling is 0.090 at the 95% confidence level. The observed upper limit on the $t \rightarrow uH$ branching ratio is $2.4 \times 10^{-3}$.

Keywords: 13 TeV,Exotic Higgs production,Higgs to 2 photons,Top properties measurements,ttbar rare decays,BSM search,Higgs,Di-photon,W,b-hadron,b-jets,Photons

05-JUL-171336.1 fb-1Documents | 1707.01404 | Inspire
Internal
HIGGPaperSearch H(125)->gamgam + Missing-ETFull Title: Search for dark matter in association with a Higgs boson decaying to two photons at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for dark matter in association with a Higgs boson decaying to two photons is presented. This study is based on data collected with the ATLAS detector, corresponding to an integrated luminosity of $36.1~\mathrm{fb}^{-1}$ of proton--proton collisions at the LHC at a center-of-mass energy of 13 TeV in 2015 and 2016. No significant excess over the expected background is observed. Upper limits at 95% confidence level are set on the visible cross section for beyond the Standard Model physics processes, and the production cross section times branching fraction of the Standard Model Higgs boson decaying into two photons in association with missing transverse momentum in three different benchmark models. Limits at 95% confidence level are also set on the observed signal in two-dimensional mass planes. Additionally, the results are interpreted in terms of 90% confidence-level limits on the dark-matter--nucleon scattering cross section, as a function of the dark-matter particle mass, for a spin-independent scenario.

Keywords: 13 TeV,Simplified DM model,Exotic Higgs production,Higgs to 2 photons,BSM search,Dark matter,Higgs,Di-photon,MET,Photons

13-JUN-171336.1 fb-1Documents | 1706.03948 | Inspire
Internal
HIGGPaperSearch H(125)->mumuFull Title: Search for the dimuon decay of the Higgs boson in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for the dimuon decay of the Higgs boson was performed using data corresponding to an integrated luminosity of 36.1 fb$^{-1}$ collected with the ATLAS detector in $pp$ collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider. No significant excess is observed above the expected background. The observed (expected) upper limit on the cross-section times branching ratio is 3.0 (3.1) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125 GeV. When combined with the $pp$ collision data at $\sqrt{s}= 7$ TeV and $\sqrt{s}=8$ TeV, the observed (expected) upper limit is 2.8 (2.9) times the Standard Model prediction.

Keywords: 13 TeV,Higgs to 2 muons,2 leptons

11-MAY-171336 fb-1Documents | 1705.04582 | Inspire
Briefing | Internal
JETMPaperPerformance of Top Quark and W Boson Tagging in Run 2 with ATLASFull Title: Performance of top-quark and $W$-boson tagging with ATLAS in Run 2 of the LHC

Abstract: The performance of taggers for hadronically decaying top quarks and $W$ bosons in $pp$ collisions at $\sqrt{s } = 13$ TeV recorded by the ATLAS experiment at the Large Hadron Collider is presented. A set of techniques based on jet shape observables are studied to determine a set of optimal cut-based taggers for use in physics analyses. The studies are extended to assess the utility of combinations of substructure observables as a multivariate tagger using boosted decision trees or deep neural networks in comparison with taggers based on two-variable combinations. In addition, for highly boosted top-quark tagging, a deep neural network based on jet constituent inputs as well as a re-optimisation of the shower deconstruction technique is presented. The performance of these taggers is studied in data collected during 2015 and 2016 corresponding to 36.1 fb$^{-1}$ for the $t\bar{t}$ and $\gamma+$jet and 36.7 fb$^{-1}$ for the dijet event topologies.

Keywords: Jet substructure

23-AUG-181336 fb-1Documents | 1808.07858 | Inspire
Internal
JETMPaperLarge-R Jet In-Situ CalibrationFull Title: In situ calibration of large-$R$ jet energy and mass in 13 TeV proton-proton collisions with the ATLAS detector

Abstract: The response of the ATLAS detector to large-radius jets is measured in situ using 36.2 fb$^{-1}$ of $\sqrt{s } = 13$ TeV proton-proton collisions provided by the LHC and recorded by the ATLAS experiment during 2015 and 2016. The jet energy scale is measured in events where the jet recoils against a reference object, which can be either a calibrated photon, a reconstructed $Z$ boson, or a system of well-measured small-radius jets. The jet energy resolution and a calibration of forward jets are derived using dijet balance measurements. The jet mass response is measured with two methods: using mass peaks formed by $W$ bosons and top quarks with large transverse momenta and by comparing the jet mass measured using the energy deposited in the calorimeter with that using the momenta of charged-particle tracks. The transverse momentum and mass responses in simulations are found to be about 2-3% higher than in data. This difference is adjusted for with a correction factor. The results of the different methods are combined to yield a calibration over a large range of transverse momenta $p_{\rm T}$. The precision of the relative jet energy scale is 1-2% for $200~{\rm GeV} < p_{\rm T} < 2~{\rm TeV}$, while that of the mass scale is 2-10%. The ratio of the energy resolutions in data and simulation is measured to a precision of 10-15% over the same $p_{\rm T}$ range.

Keywords: 13 TeV,Jet substructure,BSM search,Top pair,Z,W,Boosted,All hadronic

25-JUL-181336 fb-1Documents | 1807.09477 | Inspire
Internal
JETMConference noteObject based Missing Et SignificanceFull Title: Object based Missing Transverse Momentum Significance in the ATLAS Detector

Abstract: Missing transverse momentum, $E_{\rm T}^{\rm miss}$, is commonly used to study the production of weakly interacting particles. The missing transverse momentum significance, $\mathcal{S}$, helps to separate events in which the reconstructed ${E_{\rm T}^{\rm miss}}$ originates from weakly interacting particles, from those in which ${E_{\rm T}^{\rm miss}}$ is consistent with contributions coming from particle measurement, resolutions and inefficiencies. On an event-by-event basis, $\mathcal{S}$ evaluates the p-value that the observed ${E_{\rm T}^{\rm miss}}$ is consistent with the null hypothesis of zero real ${E_{\rm T}^{\rm miss}}$, given the full event composition. A high value of $\mathcal{S}$ is an indication that the ${E_{\rm T}^{\rm miss}}$ observed in the event is not well explained by resolution smearing alone, implying that the event is more likely to contain unseen objects such as neutrinos or more exotic weakly interacting particles. A new definition of an object-based missing transverse momentum significance variable is presented. Its performance is studied in $Z \rightarrow e e$ and $ZZ \rightarrow e e \nu \nu$ events using data collected in proton–proton collisions at a centre-of-mass energy of $13$ TeV during 2015 and 2016. Results are shown for a data sample corresponding to an integrated luminosity of $36\,\rm{fb}^{-1}$.

Keywords: 13 TeV,Etmiss performance,Top pair,Z,W,MET,2 leptons

14-JUL-181336 fb-1Documents | Internal
JETMConference noteMissing Et performance in 13 TeV dataFull Title: Performance of MissingEt in ATLAS run 2

Abstract: The reconstruction and calibration algorithms used to measure missing transverse momentum ($E_{\text{T}}^{\text{miss}}$) with the ATLAS detector utilise energy deposits within the calorimeter and tracks reconstructed in the inner detector and the muon spectrometer. The performance of the $E_{\text{T}}^{\text{miss}}$ reconstruction algorithms is evaluated using data collected in proton--proton collisions in 2015 and 2016 at a centre-of-mass energy of $13$ TeV. Results are shown for a data sample corresponding to an integrated luminosity of $36~$fb$^{-1}$. The performance of $E_{\text{T}}^{\text{miss}}$ built with jets reconstructed using a particle flow algorithm is presented and compared to that built with calorimeter jets. Various strategies are used to suppress effects arising from additional proton--proton interactions, called pileup. The tracking and vertexing information is used to distinguish contributions from pileup entering the $E_{\text{T}}^{\text{miss}}$ calculation. The modelling of $E_{\text{T}}^{\text{miss}}$ in simulated events containing a $Z$ boson decaying to two charged leptons (electrons or muons) is compared to data, and estimates of the systematic uncertainties in the $E_{\text{T}}^{\text{miss}}$ measurements are presented.

Keywords: 13 TeV,Etmiss performance,Z,W,MET,All hadronic,2 leptons

21-JUN-181336 fb-1Documents | Internal
JETMConference noteTagging of boosted top and W bosons in run 2Full Title: Performance of Top Quark and W Boson Tagging in Run 2 with ATLAS

Abstract: The performance of hadronically-decaying top-quark and $W$-boson taggers in $pp$ collisions at $\sqrt{s}$ = 13 TeV recorded by the ATLAS experiment at the Large Hadron Collider is presented. A set of techniques, including some new to the data recorded in 2015 and 2016, are studied to determine a set of optimal cut-based taggers for use in physics analyses. A further extension is made to study the utility of combinations of substructure observables as a multivariate tagger using boosted decision trees and deep neural networks in comparison with taggers based on two-variable combinations. The performance of these taggers is studied with the data collected during 2015 and 2016 in $t\bar{t}$, dijet and $\gamma$ + jet event topologies.

Keywords: 13 TeV,Jet mass scale,Jet substructure,Top pair,Z,W,Boosted,1 lepton

1335 fb-1Documents | Internal
JETMConference noteMitigating pile-up in jets before jet reconstructionFull Title: Constituent-level pileup mitigation performance using 2015 data

Abstract: Pile-up of simultaneous proton-proton collisions at the LHC has a significant impact on jet reconstruction. In this note the performance of several pile-up mitigation techniques is evaluated in detailed simulations of the ATLAS experiment. Four algorithms that act on the jet-constituent level are evaluated: SoftKiller, the cluster vertex fraction algorithm and Voronoi and constituent subtraction. We find that application of these constituent-level algorithms improves the resolution of low-transverse-momentum jets. The improvement is significant for collisions with 80-200 simultaneous proton-proton collisions envisaged in future runs of the LHC.

Keywords: 14 TeV,Jet energy calibration,HL-LHC

1332 fb-1Documents | Internal
JETMConference noteIn-situ large-R jet performanceFull Title: In-situ measurements of large-radius jet reconstruction performance

Abstract: The response of the ATLAS experiment to groomed large (R=1.0) radius jets is measured {\em in-situ} with 33 fb−1 of $\sqrt$=13 TeV LHC proton--proton collisions collected in 2016. Results from several methods are combined. The jet transverse momentum scale and resolution are measured in events where the jet recoils against a reference object, either a calibrated photon, another jet, or a recoiling system of jets. The jet mass is constrained using mass peaks formed by boosted W-bosons and top quarks and by comparison to the jet mass calculated with track jets. Generally, the Monte Carlo description is found to be adequate. Small discrepancies are incorporated as {\em in-situ} corrections. The constraint on the transverse momentum scale is 1-2% for pT< 2 TeV, that on the mass scale 2-4%. The pT (mass) resolution is constrained to 10% (20%).

Keywords: 13 TeV,Jet mass scale,Jet substructure,Jet energy calibration,Photon,>=3 jets,2 jets,Photons

19-JUL-171333 fb-1Documents | Internal
JETMConference notePerformance of jet reclustering and close-by effectsFull Title: Jet reclustering and close-by effects in ATLAS Run 2

Abstract: The reconstruction of hadronically-decaying, high-$p_{T}$ $W$, $Z$ and Higgs bosons and top quarks is instrumental to exploit the physics potential of the ATLAS detector in $pp$ collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider (LHC). The jet reclustering procedure reconstructs such objects by using calibrated anti-$k_{t}$ jets as inputs to the anti-$k_{t}$ algorithm with a larger distance parameter. The performance of these reclustered large-radius jets during LHC Run 2 is studied, and compared with that of trimmed anti-$k_{t}$ large-radius jets directly constructed from locally calibrated topological clusters. The propagation of calibrations to reclustered jets is found to be sufficient to restore their average energy and mass scales to particle level. The modelling of small-radius anti-$k_{t}$ jets in each others vicinity is studied using methods which combine tracking and calorimeter information. Systematic uncertainties resulting from the propagation of the uncertainties on the input jets to the reclustering procedure are studied. Comparisons between 33.2 fb$^{-1}$ of data collected during 2016 operations and simulation are shown, and the relative jet mass scale and resolution for reclustered and conventional jets are extracted using the forward-folding technique.

Keywords: 13 TeV,Jet mass scale,Jet substructure,Jet energy calibration,Boosted

19-JUL-171333.2 fb-1Documents | Internal
STDMPaperSame-sign WW cross section at 13 TeV   Full Title: Observation of electroweak production of a same-sign $W$ boson pair in association with two jets in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This Letter presents the observation and measurement of electroweak production of a same-sign $W$ boson pair in association with two jets using 36.1 fb$^{-1}$ of proton-proton collision data recorded at a center-of-mass energy of $\sqrt{s}=13$ TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed in the detector fiducial phase-space region, defined by the presence of two same-sign leptons, electron or muon, and at least two jets with a large invariant mass and rapidity difference. A total of 122 candidate events are observed for a background expectation of $69 \pm 7$ events, corresponding to an observed signal significance of 6.5 standard deviations. The measured fiducial signal cross section is $\sigma^{\mathrm {fid.}}= 2.89^{+0.51}_{-0.48} \mathrm{(stat.)} ^{+0.29}_{-0.28} \mathrm{(syst.)}$ fb.

Keywords: 2 leptons (same charge),VBS measurements,VBS,13 TeV,Cross-section measurement,WW,MET,2 jets

07-JUN-191335 fb-1Documents | 1906.03203 | Inspire
Internal
STDMPaperMeasurement of the vector Boson scattering of VV final states in the Semileptonic decay channel   Full Title: Search for the electroweak diboson production in association with a high-mass dijet system in semileptonic final states in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This paper reports on a search for the electroweak diboson ($WW/WZ/ZZ$) production in association with a high-mass dijet system, using data from proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV. The data, corresponding to an integrated luminosity of 35.5 fb$^{-1}$, were recorded with the ATLAS detector in 2015 and 2016 at the Large Hadron Collider. The search is performed in final states in which one boson decays leptonically, and the other boson decays hadronically. The hadronically decaying $W/Z$ boson is reconstructed as either two small-radius jets or one large-radius jet using jet substructure techniques. The electroweak production of $WW/WZ/ZZ$ in association with two jets is measured with an observed (expected) significance of 2.7 (2.5) standard deviations, and the fiducial cross section is measured to be $45.1 \pm 8.6(\mathrm{stat.}) ^{+15.9} _{-14.6} (\mathrm{syst.})$ fb.

Keywords: 13 TeV,QGC measurements,VBS measurements,Electroweak processes,VBS,ZZ,WZ,WW,2 jets,1 jet,2 leptons,1 lepton

19-MAY-191335 fb-1Documents | 1905.07714 | Inspire
Internal
STDMPaperZZ production with two charged leptons and two neutrinos in the final state at 13 TeV   Full Title: Measurement of $ZZ$ production in the $\ell\ell\nu\nu$ final state with the ATLAS detector in $pp$ collisions at $\sqrt{s } = 13$ TeV

Abstract: This paper presents a measurement of $ZZ$ production with the ATLAS detector at the Large Hadron Collider. The measurement is carried out in the final state with two charged leptons and two neutrinos, using data collected during 2015 and 2016 in $pp$ collisions at $\sqrt{s } = 13$ TeV, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. The integrated cross-sections in the total and fiducial phase spaces are measured with an uncertainty of 7% and compared with Standard Model predictions, and differential measurements in the fiducial phase space are reported. No significant deviations from the Standard Model predictions are observed, and stringent constraints are placed on anomalous couplings corresponding to neutral triple gauge-boson interactions.

Keywords: 13 TeV,TGC measurements,EFT,Differential measurement,ZZ,MET,2 leptons

17-MAY-191336 fb-1Documents | 1905.07163 | Inspire
Internal
STDMPaperMeasurement of differential W+W- production cross sections in proton-proton collisions at 13TeV with the ATLAS detectorFull Title: Measurement of fiducial and differential $W^+W^-$ production cross-sections at $\sqrt{s}= $13 TeV with the ATLAS detector

Abstract: A measurement of fiducial and differential cross-sections for $W^+W^-$ production in proton-proton collisions at $\sqrt{s}= $13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of $36.1$ fb$^{-1}$ is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as $WW\rightarrow e^{\pm}\nu\mu^{\mp}\nu$. To suppress top-quark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory.

Keywords: 13 TeV,QGC measurements,Electroweak processes,Differential measurement,WW,MET,2 leptons

10-MAY-191335 fb-1Documents | 1905.04242 | Inspire
Internal
STDMPaperMeasurement of the jet shapes at 13 TeVFull Title: Measurement of jet-substructure observables in top quark, $W$ boson and light jet production in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A measurement of jet substructure variables is presented using data collected in 2016 by the ATLAS experiment at the LHC with proton-proton collisions at $\sqrt{s}=13$ TeV. Large-radius jets groomed with the trimming and soft-drop algorithms are studied. Dedicated event selections are used to study jets produced by light quarks or gluons, and hadronically decaying top quarks and $W$ bosons. The variables measured are sensitive to pronged substructure, and therefore are typically used for tagging jets from boosted massive particles. These include the energy correlation functions and the $N$-subjettiness variables. The number of subjets and the Les Houches angularity are also considered. The distributions of the substructure variables, corrected for detector effects, are compared to the predictions of various Monte Carlo event generators. They are also compared between the large-radius jets originating from light quarks or gluons, and hadronically decaying top quarks and $W$ bosons.

Keywords: 1 jet,13 TeV,Jets and photons,Differential measurement,>=3 jets,2 jets

07-MAR-191336 fb-1Documents | 1903.02942 | Inspire
Internal
STDMPaperMeasurement of the 4 lepton invariant mass distribution at 13 TeV with the ATLAS detectorFull Title: Measurement of the four-lepton invariant mass spectrum in 13 TeV proton-proton collisions with the ATLAS detector

Abstract: A measurement of the four-lepton invariant mass spectrum is made with the ATLAS detector, using an integrated luminosity of 36.1 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}$ = 13 TeV delivered by the Large Hadron Collider. The differential cross-section is measured for events containing two same-flavour opposite-sign lepton pairs. It exhibits a rich structure, with different mass regions dominated in the Standard Model by single $Z$ boson production, Higgs boson production, and $Z$ boson pair production, and non-negligible interference effects at high invariant masses. The measurement is compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. These calculations are used to interpret the data in terms of $gg\rightarrow ZZ \rightarrow 4\ell$ and $Z \rightarrow 4\ell$ subprocesses, and to place constraints on a possible contribution from physics beyond the Standard Model.

Keywords: 13 TeV,Electroweak processes,Differential measurement,ZZ,>=3 leptons

15-FEB-191336 fb-1Documents | 1902.05892 | Inspire
Rivet | HepData | Internal
STDMPaperPrecision WZ cross sections and polarisation at 13 TeVFull Title: Measurement of $W^{\pm}Z$ production cross sections and gauge boson polarisation in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: This paper presents measurements of $W^{\pm}Z$ production cross sections in $pp$ collisions at a centre-of-mass energy of 13 TeV. The data were collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider, and correspond to an integrated luminosity of 36.1 fb$^{-1}$. The $W^{\pm}Z$ candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The measured inclusive cross section in the detector fiducial region for a single leptonic decay mode is $\sigma_{W^\pm Z \rightarrow \ell^{} \nu \ell \ell}^{\textrm{fid.} } = 63.7 \pm 1.0$ (stat.) $\pm 2.3$ (syst.) $\pm 1.4$ (lumi.) fb, reproduced by the next-to-next-to-leading-order Standard Model prediction of $61.5^{+1.4}_{-1.3}$ fb. Cross sections for $W^+Z$ and $W^-Z$ production and their ratio are presented as well as differential cross sections for several kinematic observables. An analysis of angular distributions of leptons from decays of $W$ and $Z$ bosons is performed for the first time in pair-produced events in hadronic collisions, and integrated helicity fractions in the detector fiducial region are measured for the $W$ and $Z$ bosons separately. Of particular interest, the longitudinal helicity fraction of pair-produced vector bosons is also measured.

Keywords: 13 TeV,EFT,Differential measurement,Cross-section measurement,WZ,>=3 leptons

15-FEB-1913 36.1 fb-1Documents | 1902.05759 | Inspire
Internal
STDMPaperMeasurement of VBS WZjj-EW production at 13 TeVFull Title: Observation of electroweak $W^{\pm}Z$ boson pair production in association with two jets in $pp$ collisions at $\sqrt{s } = $ 13 TeV with the ATLAS detector

Abstract: An observation of electroweak $W^{\pm}Z$ production in association with two jets in proton-proton collisions is presented. The data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of $\sqrt{s } = $ 13 TeV are used, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. Events containing three identified leptons, either electrons or muons, and two jets are selected. The electroweak production of $W^{\pm}Z$ bosons in association with two jets is measured with an observed significance of 5.3 standard deviations. A fiducial cross-section for electroweak production including interference effects is measured to be $\sigma_{WZjj\mathrm{-EW} } = 0.57 \; ^{+ 0.14} _{- 0.13} \,(\mathrm{stat.}) \; ^{+ 0.07} _{- 0.06} \,(\mathrm{syst.}) \; \mathrm{fb}$. Differential cross-sections of $W^\pm Z jj$ production for several kinematic observables are also measured.

Keywords: 13 TeV,VBS measurements,Electroweak processes,VBS,WZ,2 jets

23-DEC-181336.1 fb-1Documents | 1812.09740 | Inspire
HepData | Internal
STDMPaperProperties of g -> bb splitting with small opening angles at 13 TeVFull Title: Properties of $g\rightarrow b\bar{b}$ at small opening angles in $pp$ collisions with the ATLAS detector at $\sqrt{s}=13$ TeV

Abstract: The fragmentation of high-energy gluons at small opening angles is largely unconstrained by present measurements. Gluon splitting to $b$-quark pairs is a unique probe into the properties of gluon fragmentation because identified $b$-tagged jets provide a proxy for the quark daughters of the initial gluon. In this study, key differential distributions related to the $g\rightarrow b\bar{b}$ process are measured using 33 fb$^{-1}$ of $\sqrt{s}=13$ TeV $pp$ collision data recorded by the ATLAS experiment at the LHC in 2016. Jets constructed from charged-particle tracks, clustered with the anti-$k_t$ jet algorithm with radius parameter $R = 0.2$, are used to probe angular scales below the $R=0.4$ jet radius. The observables are unfolded to particle level in order to facilitate direct comparisons with predictions from present and future simulations. Multiple significant differences are observed between the data and parton shower Monte Carlo predictions, providing input to improve these predictions of the main source of background events in analyses involving boosted Higgs bosons decaying into $b$-quarks.

Keywords: 13 TeV,Jets and photons,Differential measurement,b-jets,>=3 jets,2 jets,1 jet

21-DEC-181333.1 fb-1Documents | 1812.09283 | Inspire
Rivet | HepData | Internal
STDMPaperZ(nunu)gamma measurement and neutral aTGC limits at 13 TeVFull Title: Z($\to \nu \nu$)$\gamma$ measurement and neutral aTGC limits at 13 TeV

Abstract: The production of $Z$ bosons in association with a high-energy photon ($Z\gamma$ production) is studied in the neutrino decay channel of the $Z$ boson using $pp$ collisions at $\sqrt{s } = 13$ TeV. The analysis uses a data sample with an integrated luminosity of 36.1 fb$^{-1}$ collected by the ATLAS detector at the LHC in 2015 and 2016. Candidate $Z\gamma$ events with invisible decays of the $Z$ boson are selected by requiring significant transverse momentum ($p_{\rm T}$) of the dineutrino system in conjunction with a single isolated photon with large transverse energy ($E_{\rm T}$). The rate of $Z\gamma$ production is measured as a function of photon $E_{\rm T}$, dineutrino system $p_{\rm T}$ and jet multiplicity. Evidence of anomalous triple gauge-boson couplings is sought in $Z\gamma$ production with photon $E_{\rm T}$ greater than 600 GeV. No excess is observed relative to the Standard Model expectation, and upper limits are set on the strength of $ZZ\gamma$ and $Z\gamma\gamma$ couplings.

Keywords: Photons,Electroweak processes,Differential measurement,Cross-section measurement,Vphoton,Photon,Z,MET,13 TeV

11-OCT-181336.6 fb-1Documents | 1810.04995 | Inspire
Internal
STDMPaperMeasurement of the jet soft drop mass at 13 TeVFull Title: A measurement of the soft-drop jet mass in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: Calculations of jet substructure observables that are accurate beyond leading-logarithm accuracy have recently become available. Such observables are significant not only for probing the collinear regime of QCD that is largely unexplored at a hadron collider, but also for improving the understanding of jet substructure properties that are used in many studies at the Large Hadron Collider. This Letter documents a measurement of the first jet substructure quantity at a hadron collider to be calculated at next-to-next-to-leading-logarithm accuracy. The normalized, differential cross-section is measured as a function of $log_{10}{\rho^2}$, where $\rho$ is the ratio of the soft-drop mass to the ungroomed jet transverse momentum. This quantity is measured in dijet events from 32.9 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton--proton collisions recorded by the ATLAS detector. The data are unfolded to correct for detector effects and compared to precise QCD calculations and leading-logarithm particle-level Monte Carlo simulations.

Keywords: 13 TeV,Jets and photons,Mass measurement,Differential measurement,Cross-section measurement,All hadronic

22-NOV-1713 32.9 fb-1Documents | 1711.08341 | Inspire
Internal
STDMPaperZZ cross-section measurement and aTGC limits at 13 TeVFull Title: $ZZ \to \ell^{+}\ell^{-}\ell^{\prime +}\ell^{\prime -}$ cross-section measurements and search for anomalous triple gauge couplings in 13 TeV $pp$ collisions with the ATLAS detector

Abstract: Measurements of $ZZ$ production in the $\ell^{+}\ell^{-}\ell^{\prime +}\ell^{\prime -}$ channel in proton-proton collisions at 13 TeV center-of-mass energy at the Large Hadron Collider are presented. The data correspond to 36.1 $\mathrm{fb}^{-1}$ of collisions collected by the ATLAS experiment in 2015 and 2016. Here $\ell$ and $\ell$ stand for electrons or muons. Integrated and differential $ZZ \to \ell^{+}\ell^{-}\ell^{\prime +}\ell^{\prime -}$ cross sections with $Z \to \ell^+\ell^-$ candidate masses in the range of 66 GeV to 116 GeV are measured in a fiducial phase space corresponding to the detector acceptance and corrected for detector effects. The differential cross sections are presented in bins of twenty observables, including several that describe the jet activity. The integrated cross section is also extrapolated to a total phase space and to all Standard-Model decays of $Z$ bosons with mass between 66 GeV and 116 GeV, resulting in a value of $17.3 \pm 0.9$ [$\pm 0.6$ (stat.) $\pm 0.5$ (syst.) $\pm 0.6$ (lumi.)] pb. The measurements are found to be in good agreement with the Standard-Model predictions. A search for neutral triple gauge couplings is performed using the transverse momentum distribution of the leading $Z$-boson candidate. No evidence for such couplings is found and exclusion limits are set on their parameters.

Keywords: 13 TeV,TGC measurements,EFT,Differential measurement,ZZ,>=3 leptons

22-SEP-171336 fb-1Documents | 1709.07703 | Inspire
Rivet | HepData | Internal
SUSYPaperGluino pair, squark pair, stop pair, R-hadron; pixel ionisation, calorimeter and muon timingFull Title: Search for heavy charged long-lived particles in the ATLAS detector in 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s } = 13$ TeV

Abstract: A search for heavy charged long-lived particles is performed using a data sample of 31.6 fb$^{-1}$ of proton-proton collisions at $\sqrt{s } = 13$ TeV collected by the ATLAS experiment at the Large Hadron Collider. The search is based on observables related to ionization energy loss and time of flight, which are sensitive to the velocity of heavy charged particles traveling significantly slower than the speed of light. Multiple search strategies for a wide range of lifetimes, corresponding to path lengths of a few meters, are defined as model-independently as possible, by referencing several representative physics cases that yield long-lived particles within supersymmetric models, such as gluinos/squarks ($R$-hadrons), charginos and staus. No significant deviations from the expected Standard Model background are observed. Upper limits at 95% confidence level are provided on the production cross sections of long-lived $R$-hadrons as well as directly pair-produced staus and charginos. These results translate into lower limits on the masses of long-lived gluino, sbottom and stop $R$-hadrons, as well as staus and charginos of 2000 GeV, 1250 GeV, 1340 GeV, 430 GeV and 1090 GeV, respectively.

Keywords: 13 TeV,Stop pair production,Squark pair production,Gluino pair production,Long-lived massive particles,BSM search,Long-lived massive particle,MET,Charged tracks

05-FEB-191336.1 fb-1Documents | 1902.01636 | Inspire
HepData | Internal
SUSYPaperChargino-neutralino pair; Higgs boson in final stateFull Title: Search for chargino and neutralino production in final states with a Higgs boson and missing transverse momentum at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search is conducted for the electroweak pair production of a chargino and a neutralino $pp \rightarrow \tilde\chi^\pm_1 \tilde\chi^0_2$, where the chargino decays into the lightest neutralino and a $W$ boson, $\tilde\chi^\pm_1 \rightarrow \tilde\chi^0_1 W^{\pm}$, while the neutralino decays into the lightest neutralino and a Standard Model-like 125 GeV Higgs boson, $\tilde\chi^0_2 \rightarrow \tilde\chi^0_1 h$. Fully hadronic, semileptonic, diphoton, and multilepton (electrons, muons) final states with missing transverse momentum are considered in this search. Higgs bosons in the final state are identified by either two jets originating from bottom quarks ($h \rightarrow b\bar{b}$), two photons ($h \rightarrow \gamma\gamma$), or leptons from the decay modes $h \rightarrow WW$, $h \rightarrow ZZ$ or $h \rightarrow \tau \tau$. The analysis is based on 36.1 fb$^{-1}$ of $\sqrt{s } = 13$ TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider. Observations are consistent with the Standard Model expectations, and 95% confidence-level limits of up to 680 GeV in $\tilde\chi^\pm_1/\tilde\chi^0_2$ mass are set in the context of a simplified supersymmetric model.

Keywords: 1 lepton,Chargino/neutralino pair production,BSM search,MET,b-jets,>=3 jets,2 jets,1 jet,13 TeV,0 jets,Photons,>=3 leptons,2 leptons

22-DEC-181336 fb-1Documents | 1812.09432 | Inspire
HepData | Internal
SUSYPaperGluino pair, squark pair; tausFull Title: Search for squarks and gluinos in final states with hadronically decaying $\tau$-leptons, jets, and missing transverse momentum using $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for supersymmetry in events with large missing transverse momentum, jets, and at least one hadronically decaying $\tau$-lepton is presented. Two exclusive final states with either exactly one or at least two $\tau$-leptons are considered. The analysis is based on proton-proton collisions at $\sqrt{s } = 13$ TeV corresponding to an integrated luminosity of 36.1 fb$^{-1}$ delivered by the Large Hadron Collider and recorded by the ATLAS detector in 2015 and 2016. No significant excess is observed over the Standard Model expectation. At 95% confidence level, model-independent upper limits on the cross section are set and exclusion limits are provided for two signal scenarios: a simplified model of gluino pair production with $\tau$-rich cascade decays, and a model with gauge-mediated supersymmetry breaking (GMSB). In the simplified model, gluino masses up to 2000 GeV are excluded for low values of the mass of the lightest supersymmetric particle (LSP), while LSP masses up to 1000 GeV are excluded for gluino masses around 1400 GeV. In the GMSB model, values of the supersymmetry-breaking scale are excluded below 110 TeV for all values of $\tan\beta$ in the range $2 \leq \tan\beta \leq 60$, and below 120 TeV for $\tan\beta>30$.

Keywords: 13 TeV,GGM/GMSB,Squark pair production,Gluino pair production,BSM search,MET,>=3 jets,2 jets,1 jet,Taus

20-AUG-181336 fb-1Documents | 1808.06358 | Inspire
HepData | Internal
SUSYPaperGluino pair, squark pair, stop pair, long-lived; pixel ionisationFull Title: Search for heavy charged long-lived particles in proton-proton collisions at $\sqrt{s } = 13$ TeV using an ionisation measurement with the ATLAS detector

Abstract: This Letter presents a search for heavy charged long-lived particles produced in proton--proton collisions at $\sqrt{s } = 13$ TeV at the LHC using a data sample corresponding to an integrated luminosity of 36.1 fb$^{-1}$ collected by the ATLAS experiment in 2015 and 2016. These particles are expected to travel with a velocity significantly below the speed of light, and therefore have a specific ionisation higher than any high-momentum Standard Model particle of unit charge. The pixel subsystem of the ATLAS detector is used in this search to measure the ionisation energy loss of all reconstructed charged particles which traverse the pixel detector. Results are interpreted assuming the pair production of $R$-hadrons as composite colourless states of a long-lived gluino and Standard Model partons. No significant deviation from Standard Model background expectations is observed, and lifetime-dependent upper limits on $R$-hadron production cross-sections and gluino masses are set, assuming the gluino always decays in two quarks and a stable neutralino. $R$-hadrons with lifetimes above 1.0 ns are excluded at the 95% confidence level, with lower limits on the gluino mass ranging between 1290 GeV and 2060 GeV. In the case of stable $R$-hadrons, the lower limit on the gluino mass at the 95% confidence level is 1890 GeV.

Keywords: 13 TeV,Stop pair production,Squark pair production,Gluino pair production,Long-lived massive particles,BSM search,Long-lived massive particle,MET,Charged tracks

13-AUG-181336 fb-1Documents | 1808.04095 | Inspire
HepData | Internal
SUSYPaperchargino-neutralino pair; 4 b-jetsFull Title: Search for pair production of higgsinos in final states with at least three $b$-tagged jets in $\sqrt{s } = 13$ TeV $pp$ collisions using the ATLAS detector

Abstract: A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos $\tilde{H}$) in gauge-mediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC $pp$ collision data at a center-of-mass energy $\sqrt{s } = 13$ TeV, the former with an integrated luminosity of 36.1 fb$^{-1}$ and the latter with 24.3 fb$^{-1}$, collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as $b$-quark jets. No significant excess is found above the predicted background. Limits on the cross-section are set as a function of the mass of the $\tilde{H}$ in simplified models assuming production via mass-degenerate higgsinos decaying to a Higgs boson and a gravitino. Higgsinos with masses between 130 and 230 GeV and between 290 and 880 GeV are excluded at the 95% confidence level. Interpretations of the limits in terms of the branching ratio of the higgsino to a $Z$ boson or a Higgs boson are also presented, and a 45% branching ratio to a Higgs boson is excluded for $m_{\tilde{H}} \approx 400$ GeV.

Keywords: 13 TeV,GGM/GMSB,Higgsino production,Chargino/neutralino pair production,BSM search,MET,b-jets

11-JUN-181336 fb-1Documents | 1806.04030 | Inspire
HepData | Internal
SUSYPaperChargino-neutralino pair; 2-3 leptons, recursive jigsawFull Title: Search for chargino-neutralino production using recursive jigsaw reconstruction in final states with two or three charged leptons in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for electroweak production of supersymmetric particles is performed in two-lepton and three-lepton final states using recursive jigsaw reconstruction. The search uses data collected in 2015 and 2016 by the ATLAS experiment in $\sqrt{s } = 13$ TeV proton-proton collisions at the CERN Large Hadron Collider corresponding to an integrated luminosity of 36.1 fb$^{-1}$. Chargino-neutralino pair production, with decays via $W/Z$ bosons, is studied in final states involving leptons and jets and missing transverse momentum for scenarios with large and intermediate mass-splittings between the parent particle and lightest supersymmetric particle, as well as for the scenario where this mass splitting is close to the mass of the $Z$ boson. The latter case is challenging since the vector bosons are produced with kinematic properties that are similar to those in Standard Model processes. Results are found to be compatible with the Standard Model expectations in the signal regions targeting large and intermediate mass-splittings, and chargino-neutralino masses up to 600 GeV are excluded at 95% confidence level for a massless lightest supersymmetric particle. Excesses of data above the expected background are found in the signal regions targeting low mass-splittings, and the largest local excess amounts to 3.0 standard deviations.

Keywords: 13 TeV,Chargino/neutralino pair production,BSM search,ISR,MET,2 jets,0 jets,>=3 leptons,2 leptons

06-JUN-181336 fb-1Documents | 1806.02293 | Inspire
HepData | Internal
SUSYPaperGluino pair, squark pair; 2 leptons, Z boson, edgeFull Title: Search for new phenomena using the invariant mass distribution of same-flavour opposite-sign dilepton pairs in events with missing transverse momentum in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

Abstract: A search for new phenomena in final states containing an $e^+e^-$ or $\mu^+\mu^-$ pair, jets, and large missing transverse momentum is presented. This analysis makes use of proton--proton collision data with an integrated luminosity of 36.1 fb$^{-1}$, collected during 2015 and 2016 at a centre-of-mass energy $\sqrt{s}$ = 13 TeV with the ATLAS detector at the Large Hadron Collider. The search targets the pair production of supersymmetric coloured particles (squarks or gluinos) and their decays into final states containing an $e^+e^-$ or $\mu^+\mu^-$ pair and the lightest neutralino ($\tilde{\chi}_1^0$) via one of two next-to-lightest neutralino ($\tilde{\chi}_2^0$) decay mechanisms: $\tilde{\chi}_2^0 \rightarrow Z \tilde{\chi}_1^0$, where the $Z$ boson decays leptonically leading to a peak in the dilepton invariant mass distribution around the $Z$ boson mass; and $\tilde{\chi}_2^0 \rightarrow \ell^+\ell^-\tilde{\chi}_1^0$ with no intermediate $\ell^+\ell^-$ resonance, yielding a kinematic endpoint in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted using simplified models, and exclude gluinos and squarks with masses as large as 1.85 TeV and 1.3 TeV at 95% confidence level, respectively.

Keywords: 13 TeV,Squark pair production,Gluino pair production,BSM search,MET,>=3 jets,2 jets,1 jet,2 leptons

29-MAY-181336 fb-1Documents | 1805.11381 | Inspire
HepData | Briefing | Internal
SUSYPaperStop pair; charm taggingFull Title: Search for supersymmetry in final states with charm jets and missing transverse momentum in 13 TeV $pp$ collisions with the ATLAS detector

Abstract: A search for supersymmetric partners of top quarks decaying as $\tilde{t}_1\to c\tilde\chi^0_1$ and supersymmetric partners of charm quarks decaying as $\tilde{c}_1\to c\tilde\chi^0_1$, where $\tilde\chi^0_1$ is the lightest neutralino, is presented. The search uses 36.1 ${\rm fb}^{-1}$ $pp$ collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider and is performed in final states with jets identified as containing charm hadrons. Assuming a 100% branching ratio to $c\tilde\chi^0_1$, top and charm squarks with masses up to 850 GeV are excluded at 95% confidence level for a massless lightest neutralino. For $m_{\tilde{t}_1,\tilde{c}_1}-m_{\tilde\chi^0_1} <$100 GeV, top and charm squark masses up to 500 GeV are excluded.

Keywords: 13 TeV,Stop pair production,BSM search,MET,c-jets,All hadronic,>=3 jets,2 jets,0 lepton

04-MAY-181336 fb-1Documents | 1805.01649 | Inspire
HepData | Briefing | Internal
SUSYPaperChargino-neutralino pair; 4 leptonsFull Title: Search for supersymmetry in events with four or more leptons in $\sqrt{s}=13$ TeV $pp$ collisions with ATLAS

Abstract: Results from a search for supersymmetry in events with four or more charged leptons (electrons, muons and taus) are presented. The analysis uses a data sample corresponding to 36.1 fb$^{-1}$ of proton--proton collisions delivered by the Large Hadron Collider at $\sqrt{s}=13$ TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying taus are designed to target a range of supersymmetric scenarios that can be either enriched in or depleted of events involving the production and decay of a $Z$ boson. Data yields are consistent with Standard Model expectations and results are used to set upper limits on the event yields from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of General Gauge Mediated supersymmetry, where higgsino masses are excluded between 110 and 295 GeV. In $R$-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1.4 TeV, 1.06 TeV, and 2.25 TeV are placed on wino, slepton and gluino masses, respectively.

Keywords: >=3 leptons,GGM/GMSB,RPV SUSY,13 TeV,Higgsino production,Chargino/neutralino pair production,BSM search,MET,Taus

10-APR-181336 fb-1Documents | 1804.03602 | Inspire
HepData | Internal
SUSYPaperGluino pair; jets, RPVFull Title: Search for R-parity-violating supersymmetric particles in multi-jet final states produced in $p$-$p$ collisions at $\sqrt{s } = 13$ TeV using the ATLAS detector at the LHC

Abstract: Results of a search for gluino pair production with subsequent R-parity-violating decays to quarks are presented. This search uses 36.1 fb$^{-1}$ of data collected by the ATLAS detector in proton--proton collisions with a center-of-mass energy of $\sqrt{s}$ = 13 TeV at the LHC. The analysis is performed using requirements on the number of jets and the number of jets tagged as containing a $b$-hadron as well as a topological observable formed by the scalar sum of masses of large-radius jets in the event. No significant excess above the expected Standard Model background is observed. Limits are set on the production of gluinos in models with the R-parity-violating decays of either the gluino itself (direct decay) or the neutralino produced in the R-parity-conserving gluino decay (cascade decay). In the gluino cascade decay model, gluinos with masses between 1000 GeV and 1875 GeV are excluded at 95\% confidence level, depending on the neutralino mass. For the gluino direct decay model, the 95\% confidence level upper limit on the cross section times branching ratio varies between 0.80 fb at $m_{\tilde{g}}$ = 900 GeV and 0.011 fb at $m_{\tilde{g}}$ = 1800 GeV.

Keywords: 13 TeV,RPV SUSY,Gluino pair production,BSM search,b-jets,All hadronic,0 lepton

10-APR-181336 fb-1Documents | 1804.03568 | Inspire
Internal
SUSYPaperStop pair; tausFull Title: Search for top squarks decaying to tau sleptons in $pp$ collisions at $\sqrt{s}\ = $ 13 TeV with the ATLAS detector

Abstract: A search for direct pair production of top squarks in final states with two tau leptons, $b$-jets, and missing transverse momentum is presented. The analysis is based on proton--proton collision data at $\sqrt{s } = 13$ TeV corresponding to an integrated luminosity of 36.1 fb$^{-1}$ recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. Two exclusive channels with either two hadronically decaying tau leptons or one hadronically and one leptonically decaying tau lepton are considered. No significant deviation from the Standard Model predictions is observed in the data. The analysis results are interpreted in terms of model-independent limits and used to derive exclusion limits on the masses of the top squark $\tilde t_1$ and the tau slepton $\tilde \tau_1$ in a simplified model of supersymmetry with a nearly massless gravitino. In this model, masses up to $m(\tilde t_1) = 1.16$ TeV and $m(\tilde \tau_1) = 1.00$ TeV are excluded at 95% confidence level.

Keywords: 1 lepton,13 TeV,GGM/GMSB,Stop pair production,BSM search,MET,b-jets,Taus

27-MAR-181336 fb-1Documents | 1803.10178 | Inspire
HepData | Internal
SUSYConference noteGluino pair, stop pair; reinterpretation in long-lived scenariosFull Title: Reinterpretation of SUSY searches in long-lived R-hadron as well as prompt and long-lived R-parity violating models

Abstract: A selection of ATLAS searches for supersymmetry (SUSY), optimized for $R$-parity-conserving and $R$-parity-violating (RPV) models, are reinterpreted in SUSY models with variable RPV-coupling strength. Depending on the coupling strength the lightest supersymmetric particle is stable at collider scales, is long-lived and decays away from the interaction point, or decays promptly. Limits are placed on simplified models of pair-produced gluinos decaying to final states enhanced or depleted with top quarks, and models of pair-produced top squarks. In a model of pair-produced gluinos decaying to final states enhanced with top quarks, a lower limit of 1.8 TeV on the gluino mass is set at 95% confidence level regardless of the RPV coupling value. Limits are set on models of gluino pair production decaying to light-flavor quarks, and models of top squark production. Limits are also placed on meta-stable gluinos decaying within the detector volume.

Keywords: 13 TeV,RPV SUSY,Stop pair production,Gluino pair production,Long-lived massive particles,BSM reinterpretation,BSM search,Long-lived massive particle

12-MAR-181336 fb-1Documents | Internal
SUSYPaperChargino-neutralino pair; 2-3 leptonsFull Title: Search for electroweak production of supersymmetric particles in final states with two or three leptons at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton--proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons.

Keywords: 13 TeV,Chargino/neutralino pair production,Slepton pair production,BSM search,MET,>=3 leptons,2 leptons

07-MAR-181336 fb-1Documents | 1803.02762 | Inspire
HepData | Briefing | Internal
SUSYPaperGluino pair, squark pair, chargino-neutralino pair; photonsFull Title: Search for photonic signatures of gauge-mediated supersymmetry in 13 TeV $pp$ collisions with the ATLAS detector

Abstract: A search is presented for photonic signatures, motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of proton--proton collision data at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 36.1 fb$^{-1}$ recorded by the ATLAS detector at the LHC, and explores models dominated by both strong and electroweak production of supersymmetric partner states. Experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon or additional jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Standard Model prediction, and 95% confidence-level upper limits of between 0.083 fb and 0.32 fb are set on the visible cross section of contributions from physics beyond the Standard Model. These results are interpreted in terms of lower limits on the masses of gluinos, squarks, and gauginos in the context of generalized models of gauge-mediated supersymmetry, which reach as high as 2.3 TeV for strongly produced and 1.3 TeV for weakly produced supersymmetric partner pairs.

Keywords: 13 TeV,GGM/GMSB,Chargino/neutralino pair production,Gluino pair production,BSM search,MET,All hadronic,Photons

09-FEB-181336 fb-1Documents | 1802.03158 | Inspire
HepData | Internal
SUSYPaperChargino-neutralino pair, slepton pair; soft leptonsFull Title: Search for electroweak production of supersymmetric states in scenarios with compressed mass spectra at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for electroweak production of supersymmetric particles in scenarios with compressed mass spectra in final states with two low-momentum leptons and missing transverse momentum is presented. This search uses proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015-2016, corresponding to 36.1 fb$^{-1}$ of integrated luminosity at $\sqrt{s}=13$ TeV. Events with same-flavor pairs of electrons or muons with opposite electric charge are selected. The data are found to be consistent with the Standard Model prediction. Results are interpreted using simplified models of R-parity-conserving supersymmetry in which there is a small mass difference between the masses of the produced supersymmetric particles and the lightest neutralino. Exclusion limits at 95% confidence level are set on next-to-lightest neutralino masses of up to 130 GeV for Higgsino production and 170 GeV for wino production, and sleptons masses of up to 180 GeV for pair production of sleptons. In the compressed mass regime, the exclusion limits extend down to mass splittings of 3 GeV for Higgsino production, 2.5 GeV for wino production, and 1 GeV for slepton production. The results are also interpreted in the context of a radiatively-driven natural supersymmetry model with non-universal Higgs boson masses.

Keywords: 13 TeV,Higgsino production,Chargino/neutralino pair production,Slepton pair production,BSM search,ISR,MET,1 jet,2 leptons

21-DEC-171336 fb-1Documents | 1712.08119 | Inspire
HepData | Briefing | Internal
SUSYPaperGluino pair, squark pair, gluino-squark; 0 leptonFull Title: Search for squarks and gluinos in final states with jets and missing transverse momentum using 36 fb$^{-1}$ of $\sqrt{s}$=13 TeV $pp$ collision data with the ATLAS detector

Abstract: A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing hadronic jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded in 2015 and 2016 by the ATLAS experiment in $\sqrt{s}$=13 TeV proton-proton collisions at the Large Hadron Collider, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. The results are interpreted in the context of various models where squarks and gluinos are pair-produced and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.03 TeV for a simplified model incorporating only a gluino and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.55 TeV are excluded if the lightest neutralino is massless. These limits substantially extend the region of supersymmetric parameter space previously excluded by searches with the ATLAS detector.

Keywords: 13 TeV,pMSSM,Squark pair production,Gluino pair production,BSM search,Boosted,MET,All hadronic,0 lepton

06-DEC-171336 fb-1Documents | 1712.02332 | Inspire
HepData | Briefing | Internal
SUSYPaperGaugino pair, gluino pair; disappearing trackFull Title: Search for long-lived charginos based on a disappearing-track signature in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: This paper presents a search for direct electroweak gaugino or gluino pair production with a chargino nearly mass-degenerate with a stable neutralino. It is based on an integrated luminosity of 36.1 $fb^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 13 TeV collected by the ATLAS experiment at the LHC. The final state of interest is a disappearing track accompanied by at least one jet with high transverse momentum from initial-state radiation or by four jets from the gluino decay chain. The use of short track segments reconstructed from the innermost tracking layers significantly improves the sensitivity to short chargino lifetimes. The results are found to be consistent with Standard Model predictions. Exclusion limits are set at 95% confidence level on the mass of charginos and gluinos for different chargino lifetimes. For a pure wino with a lifetime of about 0.2 ns, chargino masses up to 460 GeV are excluded. For the strong production channel, gluino masses up to 1.65 TeV are excluded assuming a chargino mass of 460 GeV and lifetime of 0.2 ns.

Keywords: 13 TeV,Chargino/neutralino pair production,Gluino pair production,Long-lived massive particles,BSM search,Long-lived massive particle,MET,Charged tracks

06-DEC-171336 fb-1Documents | 1712.02118 | Inspire
HepData | Internal
SUSYPaperStop pair, WIMP DM pair; 1 leptonFull Title: Search for top-squark pair production in final states with one lepton, jets, and missing transverse momentum using 36 fb$^{-1}$ of $\sqrt{s}=13$ TeV pp collision data with the ATLAS detector

Abstract: The results of a search for the direct pair production of top squarks, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, several energetic jets, and missing transverse momentum are reported. The analysis also targets spin-0 mediator models, where the mediator decays into a pair of dark-matter particles and is produced in association with a pair of top quarks. The search uses data from proton-proton collisions delivered by the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of $\sqrt{s}=13$ TeV and recorded by the ATLAS detector, corresponding to an integrated luminosity of 36 fb$^{-1}$. A wide range of signal scenarios with different mass-splittings between the top squark, the lightest neutralino and possible intermediate supersymmetric particles are considered, including cases where the W bosons or the top quarks produced in the decay chain are off-shell. No significant excess over the Standard Model prediction is observed. The null results are used to set exclusion limits at 95% confidence level in several supersymmetry benchmark models. For pair-produced top-squarks decaying into top quarks, top-squark masses up to 940 GeV are excluded. Stringent exclusion limits are also derived for all other considered top-squark decay scenarios. For the spin-0 mediator models, upper limits are set on the visible cross-section.

Keywords: 13 TeV,Simplified DM model,Wimp pair with heavy flavour production,Stop pair production,Gluino pair production,BSM search,Dark matter,Boosted,MET,b-jets,>=3 jets,2 jets,1 lepton

30-NOV-171336 fb-1Documents | 1711.11520 | Inspire
HepData | Briefing | Internal
SUSYPaperGluino pair; 0-1 leptons, many b-jetsFull Title: Search for Supersymmetry in final states with missing transverse momentum and multiple $b$-jets in proton--proton collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino ($\displaystyle\tilde\chi^0_1$) is reported. It uses LHC proton--proton collision data at a centre-of-mass energy $\sqrt{s } = 13$ TeV with an integrated luminosity of 36.1 fb$^{-1}$ collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing large missing transverse momentum and several energetic jets, at least three of which must be identified as originating from $b$-quarks. To increase the sensitivity, the sample is divided into subsamples based on the presence or absence of electrons or muons. No excess is found above the predicted background. For $\displaystyle\tilde\chi^0_1$ masses below approximately 300 GeV, gluino masses of less than 1.97 (1.92) TeV are excluded at 95% confidence level in simplified models involving the pair production of gluinos that decay via top (bottom) squarks. An interpretation of the limits in terms of the branching ratios of the gluinos into third-generation squarks is also provided. These results improve upon the exclusion limits obtained with the 3.2 fb$^{-1}$ of data collected in 2015.

Keywords: 13 TeV,Gluino pair production,BSM search,Boosted,MET,b-jets,All hadronic,>=3 jets,1 lepton,0 lepton

06-NOV-171336 fb-1Documents | 1711.01901 | Inspire
HepData | Internal
SUSYPaperWIMP DM pair + HF quarks; 0, 2 leptonsFull Title: Search for dark matter produced in association with bottom or top quarks in $\sqrt{s}$ = 13 TeV pp collisions with the ATLAS detector

Abstract: A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and missing transverse momentum are considered. The analysis uses 36.1 $fb^{-1}$ of proton-proton collision data recorded by the ATLAS experiment at $\sqrt{s}$ = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are interpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour-neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross-section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour-charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements.

Keywords: 13 TeV,Simplified DM model,Wimp pair with heavy flavour production,BSM search,Dark matter,b-jets,All hadronic,>=3 jets,2 leptons,0 lepton

31-OCT-171336 fb-1Documents | 1710.11412 | Inspire
HepData | Internal
SUSYPaperStop pair; dijet pairs, RPVFull Title: A search for pair-produced resonances in four-jet final states at $\sqrt{s}$=13 TeV with the ATLAS detector

Abstract: A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb$^{-1}$ of $\sqrt{s}= $ 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, $\tilde{t}$, which decays promptly into two quarks through $R$-parity-violating couplings. Top squarks with masses in the range 100 GeV<$m_{\tilde{t}}$<410 GeV are excluded at 95% confidence level. If the decay is into a $b$-quark and a light quark, a dedicated selection requiring two $b$-tags is used to exclude masses in the ranges 100 GeV<$m_{\tilde{t}}$<470 GeV and 480 GeV<$m_{\tilde{t}}$<610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.

<p style="font-size:0.8em;color:grey;">Keywords: 13 TeV,BSM resonance,RPV SUSY,Stop pair production,BSM search,b-jets,All hadronic,>=3 jets

19-OCT-171337 fb-1Documents | 1710.07171 | Inspire
HepData | Internal
SUSYPaperStop pair; 2 leptons, b-jets, RPVFull Title: A search for $B-L$ $R$-parity-violating top squarks in $\sqrt{s } = 13$ TeV $pp$ collisions with the ATLAS experiment

Abstract: A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an $R$-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a $b$-jet. The dataset corresponds to an integrated luminosity of 36.1 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of $\sqrt{s } = 13$ TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a $b$-quark.

Keywords: 13 TeV,RPV SUSY,Stop pair production,BSM search,b-jets,2 jets,2 leptons

16-OCT-171336 fb-1Documents | 1710.05544 | Inspire
HepData | Internal
SUSYPaperGluino pair, squark pair; displaced verticesFull Title: Search for long-lived, massive particles in events with displaced vertices and missing transverse momentum in $\sqrt{s}$ = 13 TeV $pp$ collisions with the ATLAS detector

Abstract: A search for long-lived, massive particles predicted by many theories beyond the Standard Model is presented. The search targets final states with large missing transverse momentum and at least one high-mass displaced vertex with five or more tracks, and uses 32.8 fb$^{-1}$ of $\sqrt{s}$ = 13 TeV $pp$ collision data collected by the ATLAS detector at the LHC. The observed yield is consistent with the expected background. The results are used to extract 95\% CL exclusion limits on the production of long-lived gluinos with masses up to 2.37 TeV and lifetimes of $\mathcal{O}(10^{-2})$-$\mathcal{O}(10)$ ns in a simplified model inspired by Split Supersymmetry.

Keywords: All hadronic,Gluino pair production,Displaced vertex,13 TeV,Long-lived massive particles,BSM search,Long-lived massive particle,MET

13-OCT-171333 fb-1Documents | 1710.04901 | Inspire
HepData | Internal
SUSYPaperStop pair; 0 leptonFull Title: Search for a scalar partner of the top quark in the jets plus missing transverse momentum final state at $\sqrt{s}$=13 TeV with the ATLAS detector

Abstract: A search for pair production of a scalar partner of the top quark in events with four or more jets plus missing transverse momentum is presented. An analysis of 36.1 fb$^{-1}$ of $\sqrt{s}$=13 TeV proton--proton collisions collected using the ATLAS detector at the LHC yields no significant excess over the expected Standard Model background. To interpret the results a simplified supersymmetric model is used where the top squark is assumed to decay via $\tilde{t}_1 \rightarrow t^{( * )} \tilde\chi^0_1$ and $\tilde{t}_1\rightarrow b\tilde\chi^\pm_1 \rightarrow b W^{( * )} \tilde\chi^0_1$, where $\tilde\chi^0_1$ ($\chi^\pm_1$) denotes the lightest neutralino (chargino). Exclusion limits are placed in terms of the top-squark and neutralino masses. Assuming a branching ratio of 100\% to $t \tilde\chi^0_1$, top-squark masses in the range 450--950 GeV are excluded for $\tilde\chi^0_1$ masses below 160 GeV. In the case where $m_{\tilde{t}_1}\sim m_t+m_{\tilde\chi^0_1}$, top-squark masses in the range 235--590 GeV are excluded.

Keywords: 13 TeV,Stop pair production,Gluino pair production,BSM search,Boosted,MET,b-jets,>=3 jets,0 lepton

13-SEP-171336 fb-1Documents | 1709.04183 | Inspire
HepData | Internal
SUSYPaperSbottom pair, stop pair; 0-1 leptons, b-jetsFull Title: Search for supersymmetry in events with $b$-tagged jets and missing transverse momentum in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for the supersymmetric partners of the Standard Model bottom and top quarks is presented. The search uses 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV collected by the ATLAS experiment at the Large Hadron Collider. Direct production of pairs of bottom and top squarks ($\tilde{b}_{1}$ and $\tilde{t}_{1}$) is searched for in final states with $b$-tagged jets and missing transverse momentum. Distinctive selections are defined with either no charged leptons (electrons or muons) in the final state, or one charged lepton. The zero-lepton selection targets models in which the $\tilde{b}_{1}$ is the lightest squark and decays via $\tilde{b}_{1} \rightarrow b \tilde{\chi}^{0}_{1}$, where $\tilde{\chi}^{0}_{1}$ is the lightest neutralino. The one-lepton final state targets models where bottom or top squarks are produced and can decay into multiple channels, $\tilde{b}_{1} \rightarrow b \tilde{\chi}^{0}_{1}$ and $\tilde{b}_{1} \rightarrow t \tilde{\chi}^{\pm}_{1}$, or $\tilde{t}_{1} \rightarrow t \tilde{\chi}^{0}_{1}$ and $\tilde{t}_{1} \rightarrow b \tilde{\chi}^{\pm}_{1}$, where $\tilde{\chi}^{\pm}_{1}$ is the lightest chargino and the mass difference $m_{\tilde{\chi}^{\pm}_{1}}- m_{\tilde{\chi}^{0}_{1}}$ is set to 1 GeV. No excess above the expected Standard Model background is observed. Exclusion limits at 95\% confidence level on the mass of third-generation squarks are derived in various supersymmetry-inspired simplified models.

Keywords: 13 TeV,Stop pair production,Sbottom pair production,BSM search,MET,b-jets,>=3 jets,2 jets,1 lepton,0 lepton

30-AUG-171336 fb-1Documents | 1708.09266 | Inspire
HepData | Internal
SUSYPaperGluino pair, squark pair; 1 leptonFull Title: Search for squarks and gluinos in events with an isolated lepton, jets and missing transverse momentum at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: The results of a search for squarks and gluinos in final states with an isolated electron or muon, multiple jets and large missing transverse momentum using proton--proton collision data at a center-of-mass energy of $\sqrt{s}$ = 13 TeV are presented. The dataset used was recorded during 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 36.1 $fb^{-1}$. No significant excess beyond the expected background is found. Exclusion limits at 95% confidence level are set in a number of supersymmetric scenarios, reaching masses up to 2.1 TeV for gluino pair production and up to 1.25 TeV for squark pair production.

Keywords: 13 TeV,pMSSM,Squark pair production,Gluino pair production,BSM search,MET,b-jets,>=3 jets,2 jets,1 lepton

28-AUG-171336 fb-1Documents | 1708.08232 | Inspire
HepData | Internal
SUSYPaperChargino-neutralino pair; tausFull Title: Search for the direct production of charginos and neutralinos in $\sqrt{s } = $ 13 TeV $pp$ collisions with the ATLAS detector

Abstract: A search for the direct production of charginos and neutralinos in final states with at least two hadronically decaying tau leptons is presented. The analysis uses a dataset of $pp$ collisions corresponding to an integrated luminosity of 36.1 fb$^{-1}$, recorded with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s}= $ 13 TeV. No significant deviation from the Standard Model background expectation is observed. Limits are derived in scenarios of $\tilde{\chi}_{1}^{+}\tilde{\chi}_{1}^{-}$ pair production and of $\tilde{\chi}_{1}^{\pm}\tilde{\chi}_{2}^{0}$ and $\tilde{\chi}_{1}^{+}\tilde{\chi}_{1}^{-}$ production. Chargino masses up to 630 GeV are excluded at 95\% confidence level in the scenario of direct production of $\tilde{\chi}_{1}^{+}\tilde{\chi}_{1}^{-}$ for a massless $\tilde{\chi}_{1}^{0}$. Common $\tilde{\chi}_{1}^{\pm}$, $\tilde{\chi}_{2}^{0}$ masses up to 760 GeV are excluded in the case of production of $\tilde{\chi}_{1}^{\pm}\tilde{\chi}_{2}^{0}$ and $\tilde{\chi}_{1}^{+}\tilde{\chi}_{1}^{-}$ assuming a massless $\tilde{\chi}_{1}^{0}$.

Keywords: 13 TeV,Chargino/neutralino pair production,BSM search,MET,Taus

25-AUG-171336 fb-1Documents | 1708.07875 | Inspire
HepData | Internal
SUSYPaperStop pair; 2 leptonsFull Title: Search for direct top squark pair production in final states with two leptons in $\sqrt{s } = 13$ TeV $pp$ collisions with the ATLAS detector

Abstract: The results of a search for direct pair production of top squarks in events with two opposite-charge leptons (electrons or muons) are reported, using 36.1 fb$^{-1}$ of integrated luminosity from proton--proton collisions at $\sqrt{s}=13$ TeV collected by the ATLAS detector at the Large Hadron Collider. To cover a range of mass differences between the top squark $\tilde{t}$ and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay $\tilde{t} \rightarrow b \tilde{\chi}_{1}^{\pm}$ into a $b$-quark and the lightest chargino with $\tilde{\chi}_{1}^{\pm} \rightarrow W \tilde{\chi}_{1}^{0}$, the decay $\tilde{t} \rightarrow t \tilde{\chi}_{1}^{0}$ into an on-shell top quark and the lightest neutralino, the three-body decay $\tilde{t} \rightarrow b W \tilde{\chi}_{1}^{0}$ and the four-body decay $\tilde{t} \rightarrow b \ell \nu \tilde{\chi}_{1}^{0}$. No significant excess of events is observed above the Standard Model background for any selection, and limits on top squarks are set as a function of the $\tilde{t}$ and $\tilde{\chi}_{1}^{0}$ masses. The results exclude at 95% confidence level $\tilde{\chi}_{1}^{0}$ masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches.

Keywords: 13 TeV,Stop pair production,BSM search,ISR,MET,b-jets,2 leptons

10-AUG-171336 fb-1Documents | 1708.03247 | Inspire
HepData | Internal
SUSYPaperGluino pair, squark pair; 0 lepton, high jet multiplicityFull Title: Search for new phenomena with large jet multiplicities and missing transverse momentum using large-radius jets and flavour-tagging at ATLAS in 13 TeV pp collisions

Abstract: A search is presented for particles that decay producing a large jet multiplicity and invisible particles. The event selection applies a veto on the presence of isolated electrons or muons and additional requirements on the number of b-tagged jets and the scalar sum of masses of large-radius jets. Having explored the full ATLAS 2015--2016 dataset of LHC proton--proton collisions at $\sqrt{s}$=13 TeV, which corresponds to 36.1 fb$^{-1}$ of integrated luminosity, no evidence is found for physics beyond the Standard Model. The results are interpreted in the context of simplified models inspired by R-parity-conserving and R-parity-violating supersymmetry, where gluinos are pair-produced. More generic models within the phenomenological minimal supersymmetric Standard Model are also considered.

Keywords: 13 TeV,pMSSM,Gluino pair production,BSM search,MET,b-jets,>=3 jets,0 lepton

10-AUG-171336 fb-1Documents | 1708.02794 | Inspire
HepData | Internal
SUSYPaperStop pair; Z/h bosonFull Title: Search for direct top squark pair production in events with a Higgs or $Z$ boson, and missing transverse momentum in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

Abstract: A search for direct top squark pair production resulting in events with either a same-flavour opposite-sign dilepton pair with invariant mass compatible with a $Z$ boson or a pair of jets compatible with a Standard Model (SM) Higgs boson ($h$) is presented. Requirements on additional leptons, jets, jets identified as originating from $b$-quarks, and missing transverse momentum are imposed to target the other decay products of the top squark pair. The analysis is performed using proton-proton collision data at $\sqrt{s}=13$ TeV collected with the ATLAS detector at the LHC in 2015--2016, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. No excess is observed in the data with respect to the SM predictions. The results are interpreted in two sets of models. In the first set, direct production of pairs of lighter top squarks ($\tilde{t}_1$) with long decay chains involving $Z$ or Higgs bosons is considered. The second set includes direct pair production of the heavier top squark pairs ($\tilde{t}_2$) decaying via $\tilde{t}_2 \rightarrow Z \tilde{t}_1 $ or $\tilde{t}_2 \rightarrow h \tilde{t}_1$. The results exclude at 95% confidence level $\tilde{t}_2$ and $\tilde{t}_1$ masses up to about 800 GeV, extending the exclusion region of supersymmetric parameter space covered by previous LHC searches.

Keywords: 13 TeV,Stop pair production,BSM search,MET,b-jets,>=3 jets,2 jets,>=3 leptons,1 lepton

13-JUN-171336 fb-1Documents | 1706.03986 | Inspire
HepData | Internal
SUSYPaperTwo same-sign leptons or three leptonsFull Title: Search for supersymmetry in final states with two same-sign or three leptons and jets using 36 fb$^{-1}$ of $\sqrt{s}=13$ TeV $pp$ collision data with the ATLAS detector

Abstract: A search for strongly produced supersymmetric particles using signatures involving multiple energetic jets and either two isolated same-sign leptons ($e$ or $\mu$), or at least three isolated leptons, is presented. The analysis relies on the identification of $b$-jets and high missing transverse momentum to achieve good sensitivity. A data sample of proton--proton collisions at $\sqrt{s}= 13$ TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to a total integrated luminosity of 36.1 fb$^{-1}$, is used for the search. No significant excess over the Standard Model prediction is observed. The results are interpreted in several simplified supersymmetric models featuring $R$-parity conservation or $R$-parity violation, extending the exclusion limits from previous searches. In models considering gluino pair production, gluino masses are excluded up to 1.87 TeV at 95% confidence level. When bottom squarks are pair-produced and decay to a chargino and a top quark, models with bottom squark masses below 700 GeV and light neutralinos are excluded at 95% confidence level. In addition, model-independent limits are set on a possible contribution of new phenomena to the signal region yields.

Keywords: 13 TeV,NUHM,RPV SUSY,Stop pair production,Sbottom pair production,Squark pair production,Gluino pair production,BSM search,MET,b-jets,>=3 jets,2 jets,1 jet,0 jets,>=3 leptons,2 leptons (same charge)

12-JUN-171336 fb-1Documents | 1706.03731 | Inspire
HepData | Internal
SUSYPaperGluino pair, stop pair; 1 lepton, RPVFull Title: Search for new phenomena in a lepton plus high jet multiplicity final state with the ATLAS experiment using $\sqrt{s}$ = 13 TeV proton-proton collision data

Abstract: A search for new phenomena in final states characterized by high jet multiplicity, an isolated lepton (electron or muon) and either zero or at least three b-tagged jets is presented. The search uses 36.1 fb$^{-1}$ of $\sqrt{s}$ = 13 TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider in 2015 and 2016. The dominant sources of background are estimated using parameterized extrapolations, based on observables at medium jet multiplicity, to predict the b-tagged jet multiplicity distribution at the higher jet multiplicities used in the search. No significant excess over the Standard Model expectation is observed and 95% confidence-level limits are extracted constraining four simplified models of R-parity-violating supersymmetry that feature either gluino or top-squark pair production. The exclusion limits reach as high as 2.1 TeV in gluino mass and 1.2 TeV in top-squark mass in the models considered. In addition, an upper limit is set on the cross-section for Standard Model four-top production of 60 fb (6.5 times the Standard Model prediction) at 95% confidence level. Finally, model-independent limits are set on the contribution from new phenomena to the signal-region yields.

Keywords: 13 TeV,RPV SUSY,Stop pair production,Gluino pair production,BSM search,b-jets,>=3 leptons,1 lepton

27-APR-171336 fb-1Documents | 1704.08493 | Inspire
HepData | Internal
TOPQPaperSpin correlation measurement at 13 TeVFull Title: Measurements of top-quark pair spin correlations in the $e\mu$ channel at $\sqrt{s } = 13$ TeV using $pp$ collisions in the ATLAS detector

Abstract: A measurement of observables sensitive to spin correlations in $t\bar{t}$ production is presented, using 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s } = 13$ TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the $t\bar{t}$ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is significantly higher than predicted by the generators used, but agrees well with the prediction of one of the fixed-order calculations. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.

Keywords: 2 leptons,Top properties measurements,ttbar spin correlation measurements,Differential measurement

18-MAR-191336 fb-1Documents | 1903.07570 | Inspire
Internal
TOPQPaperMeasurement of ttV in multilepton final states using 36.5fb-1 at 13 TeVFull Title: Measurement of the $t\bar{t}Z$ and $t\bar{t}W$ cross sections in proton--proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A measurement of the associated production of a top-quark pair ($t\bar{t}$) with a vector boson ($W$, $Z$) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using $36.1$ fb$^{-1}$ of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The $t\bar{t}Z$ and $t\bar{t}W$ production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are $\sigma_{t\bar{t}Z } = 0.95 \pm 0.08_{\mathrm{stat.}} \pm 0.10_{\mathrm{syst.}}$ pb and $\sigma_{t\bar{t}W } = 0.87 \pm 0.13_{\mathrm{stat.}} \pm 0.14_{\mathrm{syst.}}$ pb in agreement with the Standard Model predictions. The measurement of the $t\bar{t}Z$ cross section is used to set constraints on effective field theory operators which modify the $t\bar{t}Z$ vertex.

Keywords: 2 leptons (same charge),Top properties measurements,ttbar + boson measurements,EFT,>=3 leptons

11-JAN-191336 fb-1Documents | 1901.03584 | Inspire
Internal
TOPQPaperSearch for flavor-changing neutral current t to Hq with H->b-bbar and tautau at 13 TeVFull Title: Search for top-quark decays $t \rightarrow Hq$ with 36 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for flavour-changing neutral current decays of a top quark into an up-type quark ($q=u, c$) and the Standard Model Higgs boson, $t\rightarrow Hq$, is presented. The search is based on a dataset of $pp$ collisions at $\sqrt{s}=13$ TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb$^{-1}$. Two complementary analyses are performed that search for top-quark pair events in which one top quark decays into $Wb$ and the other top quark decays into $Hq$, and target the $H\rightarrow b\bar{b}$ and $H\rightarrow\tau^+\tau^-$ decay modes, respectively. The high multiplicity of $b$-quark jets, or the presence of hadronically decaying $\tau$-leptons, are exploited in the two analyses respectively. Multivariate techniques are used to separate the signal from the background, which is dominated by top-quark pair production. No significant excess of events above the background expectation is found, and 95% CL upper limits on the $t\rightarrow Hq$ branching ratios are derived. The combination of these searches with ATLAS searches in diphoton and multilepton final states yields observed (expected) 95% CL upper limits on the $t\rightarrow Hc$ and $t\rightarrow Hu$ branching ratios of $1.1 \times 10^{-3}$ ($8.3 \times 10^{-4}$) and $1.2 \times 10^{-3}$ ($8.3 \times 10^{-4}$), respectively. The corresponding combined observed (expected) upper limits on the $|\lambda_{tcH}|$ and $|\lambda_{tuH}|$ couplings are 0.064 (0.055) and 0.066 (0.055), respectively.

Keywords: 1 lepton,Higgs to tautau,Higgs to bb,Top properties measurements,ttbar rare decays,EFT,FCNC,13 TeV,Higgs,b-jets,Taus

30-DEC-181336 fb-1Documents | 1812.11568 | Inspire
Internal
TOPQPaperMeasurement of the ttbar+gamma cross section at 13 TeVFull Title: Measurements of inclusive and differential fiducial cross-sections of $t\bar{t}\gamma$ production in leptonic final states at $\sqrt{s } = 13$ TeV in ATLAS

Abstract: Inclusive and differential cross-sections for the production of a top-quark pair in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 36.1 fb$^{-1}$, collected by the ATLAS detector at the LHC in 2015 and 2016 at a centre-of-mass energy of 13 TeV. The measurements are performed in single-lepton and dilepton final states in a fiducial volume. Events with exactly one photon, one or two leptons, a channel-dependent minimum number of jets, and at least one $b$-jet are selected. Neural network algorithms are used to separate the signal from the backgrounds. The fiducial cross-sections are measured to be 521 $\pm$ 9(stat.) $\pm$ 41(sys.) fb and 69 $\pm$ 3(stat.) $\pm$ 4(sys.) fb for the single-lepton and dilepton channels, respectively. The differential cross-sections are measured as a function of photon transverse momentum, photon absolute pseudorapidity, and angular distance between the photon and its closest lepton in both channels, as well as azimuthal opening angle and absolute pseudorapidity difference between the two leptons in the dilepton channel. All measurements are in agreement with the theoretical predictions.

Keywords: 1 lepton,Top properties measurements,ttbar + boson measurements,Differential measurement,Photons,2 leptons

04-DEC-181336 fb-1Documents | 1812.01697 | Inspire
Internal
TOPQPaperMeasurement of the ttbb cross section at 13 TeVFull Title: Measurements of fiducial and differential cross-sections of $t\bar{t}$ production with additional heavy-flavour jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: This note presents measurements of $t\bar{t}$ production in association with additional $b$-jets in $pp$ collisions at the LHC at a centre-of-mass energy of 13 TeV. Fiducial cross-section measurements are performed in the dilepton and lepton-plus-jets $t\bar{t}$ decay channels. Results are presented at particle level in the form of inclusive cross-sections of $t\bar{t}$ final states with three and four $b$-jets as well as differential cross-sections as a function of global event properties and properties of $b$-jet pairs. The measured inclusive fiducial cross-sections generally exceed the $t\bar{t}b\bar{b}$ predictions from various next-to-leading-order matrix element calculations matched to a parton shower, but are compatible within the total uncertainties. The experimental uncertainties are smaller than the ones on the predictions. Comparisons to state-of-the-art theoretical predictions with the differential measurements are shown and good agreement with data is found for most of them.

Keywords: 1 lepton,ttbar + heavy flavour measurements,ttbar cross-section measurements,Differential measurement,2 leptons

29-NOV-181336 fb-1Documents | 1811.12113 | Inspire
HepData | Internal
TOPQPaperQuantum Interference Between Single and Doubly Resonant Top Quark ProductionFull Title: Probing the quantum interference between singly and doubly resonant top-quark production in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This Letter presents a normalized differential cross-section measurement in a fiducial phase-space region where interference effects between top-quark pair production and associated production of a single top quark with a $W$ boson and a $b$-quark are significant. Events with exactly two leptons ($ee$, $\mu\mu$, or $e\mu$) and two $b$-tagged jets that satisfy a multi-particle invariant mass requirement are selected from $36.1$ fb$^{-1}$ of proton-proton collision data taken at $\sqrt{s}=13$ TeV with the ATLAS detector at the LHC in 2015 and 2016. The results are compared with predictions from simulations using various strategies for the interference. The standard prescriptions for interference modeling are significantly different from each other but are within $2\sigma$ of the data. State-of-the-art predictions that naturally incorporate interference effects provide the best description of the data in the measured region of phase space most sensitive to these effects. These results provide an important constraint on interference models and will guide future model development and tuning.

Keywords: 2 leptons,Single top Wt-channel,Single top measurements,Differential measurement

12-JUN-181336 fb-1Documents | 1806.04667 | Inspire
Internal
TOPQPaperSearch for FCNC tqH with H->WW at 13 TeVFull Title: Search for flavor-changing neutral currents in top quark decays $t\to Hc$ and $t \to Hu$ in multilepton final states in proton-proton collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector

Abstract: Flavor-changing neutral currents are not present in the Standard Model at tree level and are suppressed in loop processes by the unitarity of the Cabibbo--Kobayashi--Maskawa matrix; the corresponding rates for top quark decay processes are experimentally unobservable. Extensions of the Standard Model can generate new flavor-changing neutral current processes, leading to signals which, if observed, would be unambiguous evidence of new interactions. A dataset corresponding to an integrated luminosity of 36.1 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt{s}= $ 13 TeV recorded with the ATLAS detector at the Large Hadron Collider is used to search for top quarks decaying to up or charm quarks with the emission of a Higgs boson, with subsequent Higgs boson decay to final states with at least one electron or muon. No signal is observed and limits on the branching fractions $\mathcal{B}(t \to Hc)

Keywords: 13 TeV,Higgs to WW,Top properties measurements,ttbar rare decays,EFT,FCNC,>=3 leptons,2 leptons (same charge)

09-MAY-181336 fb-1Documents | 1805.03483 | Inspire
Internal
TOPQPaperMeasurement of color flow in ttbar at 13 TeVFull Title: Measurement of colour flow using jet-pull observables in $t\bar{t}$ events with the ATLAS experiment at $\sqrt{s } = 13$ TeV

Abstract: Previous phenomenological studies and measurements have shown that weighted angular moments derived from jet constituents encode the colour connections between initiating partons that seed the jets. This paper presents measurements of two such distributions, the jet-pull angle and jet-pull magnitude, both of which are derived from the jet-pull angular moment. The measurement is performed in $t\bar{t}$ events with one leptonically decaying $W$ boson and one hadronically decaying $W$ boson, using $36.1$ fb$^{-1}$ of $pp$ collision data recorded by the ATLAS detector at $\sqrt{s } = 13$ TeV delivered by the Large Hadron Collider. The observables are measured for two dijet systems, corresponding to the colour-connected daughters of the $W$ boson and the two $b$-jets from the top-quark decays. To allow the comparison of the measured distributions to colour model predictions, the measured distributions are unfolded to stable-particle level, after correcting for experimental effects introduced by the detector. While good agreement can be found for some combinations of predictions and observables, none of the predictions describes the data well across all observables.

Keywords: Top properties measurements,Differential measurement,1 lepton,Other top properties

08-MAY-181336 fb-1Documents | 1805.02935 | Inspire
Internal
TOPQPaperSearch for flavour-changing neutral current top quark decays t->qZ at 13 TeVFull Title: Search for flavour-changing neutral current top-quark decays $t\to qZ$ in proton--proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for flavour-changing neutral-current processes in top-quark decays is presented. Data collected with the ATLAS detector from proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of $ \sqrt{s}=13 $ TeV, corresponding to an integrated luminosity of 36.1 fb$^{−1}$, are analysed. The search is performed using top-quark pair events, with one top quark decaying through the t → qZ (q = u, c) flavour-changing neutral-current channel, and the other through the dominant Standard Model mode t → bW. Only Z boson decays into charged leptons and leptonic W boson decays are considered as signal. Consequently, the final-state topology is characterized by the presence of three isolated charged leptons (electrons or muons), at least two jets, one of the jets originating from a b-quark, and missing transverse momentum from the undetected neutrino. The data are consistent with Standard Model background contributions, and at 95% confidence level the search sets observed (expected) upper limits of 1.7 × 10$^{−4}$ (2.4 × 10$^{−4}$) on the t → uZ branching ratio and 2.4 × 10$^{−4}$ (3.2 × 10$^{−4}$) on the t → cZ branching ratio, constituting the most stringent limits to date.

Keywords: >=3 leptons,Top properties measurements,ttbar rare decays,EFT

26-MAR-181336 fb-1Documents | 1803.09923 | Inspire
Internal
TOPQPaperDifferential ttbar cross-section all-hadronic boosted 13 TeVFull Title: Measurements of $t\bar{t}$ differential cross-sections of highly boosted top quarks decaying to all-hadronic final states in $pp$ collisions at $\sqrt{s}=13\,$ TeV using the ATLAS detector

Abstract: Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and tt¯ system kinematic observables using proton-proton collisions at a center-of-mass energy of s=13  TeV. The data set corresponds to an integrated luminosity of 36.1  fb-1, recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Events with two large-radius jets in the final state, one with transverse momentum pT>500  GeV and a second with pT>350  GeV, are used for the measurement. The top-quark candidates are separated from the multijet background using jet substructure information and association with a b-tagged jet. The measured spectra are corrected for detector effects to a particle-level fiducial phase space and a parton-level limited phase space, and are compared to several Monte Carlo simulations by means of calculated χ2 values. The cross-section for tt¯ production in the fiducial phase-space region is 292±7(stat)±71(syst)  fb, to be compared to the theoretical prediction of 384±36  fb.

Keywords: All hadronic,ttbar cross-section measurements,Top pair production,Differential measurement,Boosted

06-JAN-181336 fb-1Documents | 1801.02052 | Inspire
Rivet | HepData | Briefing | Internal
TOPQPaperMeasurement of tW single top differential cross-sections at 13 TeVFull Title: Measurement of differential cross-sections of a single top quark produced in association with a $W$ boson at $\sqrt{s}=13$ TeV with ATLAS

Abstract: The differential cross-section for the production of a $W$ boson in association with a top quark is measured for several particle-level observables. The measurements are performed using 36.1 fb$^{-1}$ of $pp$ collision data collected with the ATLAS detector at the LHC in 2015 and 2016. Differential cross-sections are measured in a fiducial phase space defined by the presence of two charged leptons and exactly one jet matched to a $b$-hadron, and are normalised with the fiducial cross-section. Results are found to be in good agreement with predictions from several Monte Carlo event generators.

Keywords: 2 leptons,Single top Wt-channel,Single top measurements,MVA / machine learning,Differential measurement,Cross-section measurement

05-DEC-171336 fb-1Documents | 1712.01602 | Inspire
HepData | Briefing | Internal
TOPQPapertZ cross section in the trilepton channel at 13 TeVFull Title: Measurement of the production cross-section of a single top quark in association with a $Z$ boson in proton-proton collisions at 13 TeV with the ATLAS detector

Abstract: The production of a top quark in association with a $Z$ boson is investigated. The proton--proton collision data collected by the ATLAS experiment at the LHC in 2015 and 2016 at a centre-of-mass energy of $\sqrt{s } = 13 \mathrm{TeV}$ are used, corresponding to an integrated luminosity of $36.1 \mathrm{fb}^{-1}$. Events containing three identified leptons (electrons and/or muons) and two jets, one of which is identified as a $b$-quark jet are selected. The major backgrounds are diboson, $t\bar{t}$ and $Z\mathrm{+jets}$ production. A neural network is used to improve the background rejection and extract the signal. The resulting significance is $4.2\sigma$ in the data and the expected significance is $5.4\sigma$. The measured cross-section for $tZq$ production is $600 \pm 170 \mathrm{(stat.)} \pm 140 \mathrm{(syst.)} \mathrm{fb}$.

Keywords: >=3 leptons,Single top measurements,MVA / machine learning,Cross-section measurement

10-OCT-171336 fb-1Documents | 1710.03659 | Inspire
Briefing | Internal
TRIGConference noteThe ATLAS Tau Trigger in Run 2Full Title: The ATLAS Tau Trigger in Run-2

Abstract: This note describes the algorithms and selections used in the ATLAS experiment to trigger on hadronically decaying tau leptons in the LHC Run~2. The performances of the tau trigger in the $33\,\mathrm{fb}^{-1}$ of $pp$ collision data recorded in 2016 at $\sqrt{s}=13$ TeV are documented.

Keywords: Taus,Tau trigger,13 TeV

12-JUL-171333 fb-1Documents | Internal

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Topic revision: r89 - 2018-06-02 - AndreasHoecker
 
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