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Summary of ATLAS 13 TeV results using the full 2015−2018 (Run 2) dataset

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 between 2015 and 2018. 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.

Physics results

  GroupFormatShort TitleDate√s (TeV)LLinks
SUSYPaperGluino pair; squark pair; gluino-squark; 0-lepton   Full Title: Search for squarks and gluinos in final states with jets and missing transverse momentum using 139 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 jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$^{-1}$. The results are interpreted in the context of various $R$-parity-conserving models where squarks and gluinos are produced in pairs or in association and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.30 TeV for a simplified model containing only a gluino and the lightest neutralino, assuming the latter is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.85 TeV are excluded if the lightest neutralino is massless. These limits extend substantially beyond the region of supersymmetric parameter space excluded previously by similar searches with the ATLAS detector.

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

27-OCT-2013139 fb-1Documents
HepData | Internal
HIGGPaperVBF H(125) -> bb (photon-tagged)   Full Title: Search for Higgs boson production in association with a high-energy photon via vector-boson fusion with decay into bottom quark pairs at $\sqrt{s}$=13 TeV with the ATLAS detector

Abstract: A search is presented for the production of the Standard Model Higgs boson in association with a high-energy photon. With a focus on the vector-boson fusion process and the dominant Higgs boson decay into $b$-quark pairs, the search benefits from a large reduction of multijet background compared to more inclusive searches. Results are reported from the analysis of 132 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV collected with the ATLAS detector at the LHC. The measured Higgs boson signal yield in this final-state signature is $1.3 \pm 1.0$ times the Standard Model prediction. The observed significance of the Higgs boson signal above the background is 1.3 standard deviations, compared to an expected significance of 1.0 standard deviations.

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

26-OCT-2013139 fb-1Documents | 2010.13651
Internal
EXOTPaperMono-scalar to VV in hadronic channel   Full Title: Search for dark matter produced in association with a dark Higgs boson decaying into $W^\pm W^\mp$ or $ZZ$ in fully hadronic final states from $\sqrt{s}=13$ TeV $pp$ collisions recorded with the ATLAS detector

Abstract: Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with $VV=W^\pm W^\mp$ or $ZZ$ pairs from a decay of a dark Higgs boson $s$ is searched for using 139 fb$^{-1}$ of $pp$ collisions recorded by the ATLAS detector at a center-of-mass energy of 13 TeV. The $s\to V(q\bar q)V(q\bar q)$ decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted $VV$ pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with $m_s > 160$ GeV are excluded.

Keywords: 13 TeV,BSM search,Dark matter,W,Boosted,MET,>=3 jets

13-OCT-2013139 fb-1Documents | 2010.06548 | Inspire
Internal
STDMPaperObservation of yy->WW   Full Title: Observation of photon-induced $W^+W^-$ production in $pp$ collisions at $\sqrt{s}=13$ TeV using the ATLAS detector

Abstract: This letter reports the observation of photon-induced production of $W$-boson pairs, $\gamma\gamma\rightarrow WW$. The analysis uses 139 fb$^{-1}$ of LHC proton-proton collision data taken at $\sqrt{s}=13$ TeV recorded by the ATLAS experiment during the years 2015-2018. The measurement is performed selecting one electron and one muon, corresponding to the decay of the diboson system as  $WW\rightarrow e^\pm\nu\mu^\mp\nu$ final state. The background-only hypothesis is rejected with a significance of 8.4 standard deviations which is consistent within uncertainty with the expectation from Monte Carlo simulation. A cross section for the $\gamma\gamma\rightarrow WW$ process of $3.13\pm0.31\mathrm{(stat.)}\pm0.28\mathrm{(syst.)}$ fb is measured in a fiducial volume close to the acceptance of the detector, by requiring  an electron and a muon of opposite signs with large dilepton transverse momentum and exactly zero additional charged particles.

Keywords: 13 TeV,Electroweak processes,Cross-section measurement,WW,2 leptons

08-OCT-2013139 fb-1Documents | 2010.04019 | Inspire
Internal
EXOTPaperLepton Flavor Violating Z Decay with a Hadronic Tau   Full Title: Charged-lepton-flavour violation at the LHC: a search for $Z\to e\tau/\mu\tau$ decays with the ATLAS detector

Abstract: In the Standard Model of particle physics, leptons are key building blocks of matter and come in three families (flavours). Leptons of different flavours have the same properties, except for their mass. In addition, the number of leptons in each family is conserved in interactions. Such conservation is known as lepton flavour conservation, and no fundamental principles impose it. Since the formulation of the Standard Model, the observation of flavour oscillations among neutrinos (the neutral leptons) has demonstrated that neutrinos have mass and in neutrino weak interactions the lepton flavour is not conserved. To date, there is no experimental evidence that lepton flavour violation occurs in interactions between charged leptons, and an observation of such a phenomenon would be an exciting sign of new particles or new type of interactions beyond the Standard Model. The ATLAS experiment at the Large Hadron Collider at CERN sets a new constraint on lepton-flavour-violating effects in weak interactions, searching for $Z$-boson decays into a $\tau$-lepton and another lepton of different flavour ($e$ or $\mu$) with opposite electric charge. The branching fractions for these decays are now measured by the ATLAS experiment to be less than $8.1\times10^{-6}$ ($e\tau$) and $9.5\times10^{-6}$ ($\mu\tau$) at 95% confidence level, using 139 $fb^{-1}$ of proton-proton collision data at centre-of-mass energy $\sqrt{s}=13$ TeV and 20.3 $fb^{-1}$ at $\sqrt{s}=8$ TeV. These results supersede the best limits set by the LEP experiments more than two decades ago.

Keywords: 13 TeV,Other new particle searches,LFV,Z,Taus,2 leptons

06-OCT-2013139 fb-1Documents | 2010.02566 | Inspire
Internal
EXOTPaperSearch for pair-produced LQs in tl tl final state   Full Title: Search for pair production of scalar leptoquarks decaying into first- or second-generation leptons and top quarks in proton-proton collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for pair production of scalar leptoquarks, each decaying into either an electron or a muon and a top quark, is presented.  This is the first leptoquark search using ATLAS data to investigate top-philic cross-generational couplings that could provide explanations for recently observed anomalies in $B$ meson decays. This analysis targets high leptoquark masses which cause the decay products of each resultant top quark to be contained within a single high-$p_{\mathrm{T}}$ large-radius jet. The full Run 2 dataset is exploited, consisting of 139 fb$^{-1}$ of data collected from proton-proton collisions at $\sqrt{s}=13$ TeV from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. In the absence of any significant deviation from the background expectation, lower limits on the leptoquark masses are set at 1480 GeV and 1470 GeV for the electron and muon channel, respectively.

Keywords: 13 TeV,Leptoquarks,BSM search,Top pair,Boosted,2 jets,2 leptons

05-OCT-2013139 fb-1Documents | 2010.02098 | Inspire
Internal
SUSYConference noteSearch for displaced leptons   Full Title: Search for displaced leptons in sqrt(s) = 13 TeV pp collisions with the ATLAS detector

Abstract: A search for charged leptons with large impact parameters using 139 fb$^{-1}$ of $\sqrt{s } =  13$ TeV $pp$ data from the ATLAS detector at the LHC is presented, addressing a long-standing gap in coverage of possible new physics signatures. Results are consistent with the background prediction. This search provides unique sensitivity to long-lived scalar supersymmetric lepton-partners (sleptons). For 0.1 ns lifetimes selectron, smuon and stau masses up to 720 GeV, 680 GeV, and 340 GeV are excluded, respectively, at 95% CL drastically improving on the previous best limits from LEP.

Keywords: 13 TeV,Displaced vertex,GGM/GMSB,RPV SUSY,Slepton pair production,Long-lived massive particles,BSM search,Long-lived massive particle,2 leptons

05-OCT-2013139 fb-1Documents | Briefing | Internal
SUSYPaperSearch for new physics in final states with large b-jet multiplicity   Full Title: Search for phenomena beyond the Standard Model in events with large $b$-jet multiplicity using the ATLAS detector at the LHC

Abstract: A search is presented for new phenomena in events characterised by high jet multiplicity, no leptons (electrons or muons), and four or more jets  originating from the fragmentation of $b$-quarks ($b$-jets). The search uses 139 fb$^{-1}$ of $\sqrt{s}$ = 13 TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider during Run 2. The dominant Standard Model background originates from multijet production and is estimated using a data-driven technique based on an extrapolation from events with low $b$-jet multiplicity to the high $b$-jet multiplicities used in the search. No significant excess over the Standard Model expectation is observed and 95% confidence-level limits that constrain  simplified models of R-parity-violating supersymmetry are determined. The exclusion limits reach 950 GeV in top-squark mass in the models considered.

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

02-OCT-2013139 fb-1Documents | 2010.01015 | Inspire
Internal
HIGGPaperSearch BSM H->ZZ->4l+llnunu   Full Title: Search for  heavy resonances decaying into a pair of $Z$ bosons in the $\ell^+\ell^-\ell^+\ell^-$ and  $\ell^+\ell^-\nu\bar\nu$ final states using 139Search for  heavy  fb$^{-1}$ of 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 collected from 2015 to 2018 that corresponds to the full integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. Different mass ranges spanning 200 GeV to 2000 GeV for the hypothetical resonances are considered, depending on the final state and model. In the absence of a significant observed excess, 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, and the limits 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 4 lepton,BSM search,ZZ,>=3 leptons

30-SEP-2013139 fb-1Documents | 2009.14791 | Inspire
Internal
EXOTPaperHeavy Lepton Multiplet Search in 2 lepton final stateFull Title: Search for type-III seesaw heavy leptons in dilepton final states in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to 139 fb$^{-1}$ of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on the final state with two light leptons (electrons or muons) of different flavour and charge combinations, with at least two jets and large missing transverse momentum. No significant excess over the Standard Model expectation is observed. The results are translated into exclusion limits on heavy-lepton masses, and the observed lower limit on the mass of the type-III seesaw heavy leptons is 790 GeV at 95% confidence level.

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

18-AUG-2013139 fb-1Documents | 2008.07949 | Inspire
Internal
SUSYPaperGluino pair, 0 lepton, large jet multiplicityFull Title: Search for new phenomena in final states with large jet multiplicities and missing transverse momentum using $\sqrt{s } =  13$ TeV proton$-$proton collisions recorded by ATLAS in Run 2 of the LHC

Abstract: Results of a search for new particles decaying into eight or more jets and moderate missing transverse momentum are presented. The analysis uses 139 fb$^{-1}$ of proton$-$proton collision data at $\sqrt{s } =  13$ TeV collected by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. The selection rejects events containing isolated electrons or muons, and makes requirements according to the number of $b$-tagged jets and the scalar sum of masses of large-radius jets. The search extends previous analyses both in using a larger dataset and by employing improved jet and missing transverse momentum reconstruction methods which more cleanly separate signal from background processes. No evidence for physics beyond the Standard Model is found. The results are interpreted in the context of supersymmetry-inspired simplified models, significantly extending the limits on the gluino mass in those models. In particular, limits on the gluino mass are set at 2 TeV when the lightest neutralino is nearly massless in a model assuming a two-step cascade decay via the lightest chargino and second-lightest neutralino.

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

14-AUG-2013139 fb-1Documents | 2008.06032 | Inspire
Internal
HDBSPaperSearch for Hgamma resonancesFull Title: Search for heavy resonances decaying into a photon and a hadronically decaying Higgs boson in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This Letter presents a search for the production of new heavy resonances decaying into a Higgs boson and a photon using proton-proton collision data at $\sqrt{s}=13$ TeV collected by the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 139 fb$^{-1}$. The analysis is performed by reconstructing hadronically decaying Higgs boson $(H\to b\bar{b})$ candidates as single large-radius jets. A novel algorithm using information about the jet constituents in the center-of-mass frame of the jet is implemented to identify the two $b$-quarks in the single jet. No significant excess of events is observed above the expected background. Upper limits are set on the production cross-section times branching fraction for narrow spin-1 resonances decaying into a Higgs boson and a photon in the resonance mass range from 0.7 to 4 TeV, cross-sections times branching fraction are excluded between 11.6 fb and 0.11 fb at a 95% confidence level.

Keywords: 13 TeV,BSM resonance,BSM search,Higgs,Boosted,b-jets,Photons

13-AUG-2013139 fb-1Documents | 2008.05928 | Inspire
HepData | Internal
HIGGPaperVH(125) H->bb boostedFull Title: Measurement of the associated production of a Higgs boson decaying into $b$-quarks with a vector boson at high transverse momentum in $pp$ collisions at $\sqrt{s } =  13$ TeV with the ATLAS detector

Abstract: The associated production of a Higgs boson with a $W$ or $Z$ boson decaying into leptons and where the Higgs boson decays to a $b\bar{b}$ pair is measured in the high vector-boson transverse momentum regime, above 250 GeV, with the ATLAS detector. The analysed data, corresponding to an integrated luminosity of 139 fb$^{-1}$, were collected in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at a centre-of-mass energy of $\sqrt{s } =  13$ TeV. The measured signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model, is $0.72 ^{+0.39}_{-0.36}$ corresponding to an observed (expected) significance of 2.1 (2.7) standard deviations. Cross-sections of associated production of a Higgs boson decaying into $b$ quark pairs with a $W$ or $Z$ gauge boson, decaying into leptons, are measured in two exclusive transverse momentum regions, 250-400 GeV and above 400 GeV, and interpreted as constraints on anomalous couplings in the framework of a Standard Model effective field theory.

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

04-AUG-2013139 fb-1Documents | 2008.02508 | Inspire
Briefing | Internal
HIGGConference noteH(125)->gammagamma STXS and couplingsFull Title: Measurement of the properties of Higgs boson production st $\sqrt{s} $ 13 TeV in the $H\to\gamma\gamma$ channel using 139 fb$^{-1}$ of $pp$ collision data with the ATLAS experiment

Abstract: Measurements of Higgs boson production cross sections are carried out in the diphoton decay channel using 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 13 TeV collected by the ATLAS experiment. The total Higgs boson production cross-section in the Higgs boson rapidity range $|y_H|<2.5$ times its diphoton decay branching ratio is measured to be $127 \pm 10$ fb. Cross-sections for gluon fusion, weak vector boson fusion, associated production with a $W$ or $Z$ boson, and top associated production processes are reported. An upper limit of eight times the Standard Model prediction is set for the associated production of a Higgs boson with a single top quark process. Higgs boson production is further characterized through measurements of the Simplified Template Cross-Sections (STXS). In total, cross-sections of 27 STXS regions are measured. The level of compatibility between the measured STXS cross-sections and their Standard Model predictions is $60\%$.

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,VBF,Gluon fusion,Cross-section measurement,Higgs,Di-photon,Photons

01-AUG-2013139 fb-1Documents | Internal
HIGGConference noteSearch BSM H-> gamma gammaFull Title: Search for resonances decaying to photon pairs in 139 fb$^{-1}$ of pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: Searches for new resonances in the diphoton final state, with spin-0 as predicted by theories with an extended Higgs sector and with spin-2 using a warped extra-dimension benchmark model, are presented using 139 fb$^{-1}$ of $\sqrt{s } = $ 13TeV $pp$ collision data collected the ATLAS experiment at the LHC. No significant deviation from the Standard Model is observed and upper limits are placed on the production cross-section times branching ratio to two photons as a function of the resonance mass.

Keywords: 13 TeV,BSM Higgs searches,Higgs to 2 photons,BSM search,Di-photon,Photon,Photons

01-AUG-2013139 fb-1Documents | Internal
EXOTConference noteMonojet searchFull Title: Search for new physics in events with jets andmissing transverse momentum in p p collisions at $\sqrt(s) = 13$ with the ATLAS detector

Abstract: Search for new phenomena in events with jets and missing transverse momentum in p p collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector An overall agreement is observed between the number of events in data and Standard Model predictions. Model-independent $95\%$ confidence level limits on visible cross sections for new processes are obtained in the range between 861 fb and 0.3 fb. Results are also translated into improved exclusion limits in models with pair-produced weakly interacting dark-matter candidates, large extra spatial dimensions, supersymmetric particles in several compressed scenarios, axion-like particles, and new scalar particles in dark-energy inspired models. In addition, the data are translated into bounds on the invisible branching ratio of the Higgs boson.

Keywords: 13 TeV,Other new particle searches,BSM search,ISR,Dark matter,MET,All hadronic,1 jet,0 lepton

31-JUL-2013139 fb-1Documents | Briefing | Internal
HDBSConference noteSearch for heavy H+->tbFull Title: Search for heavy H+->tb produced in association with a top

Abstract: This paper presents a search for charged Higgs bosons heavier than the top quark and decaying into a pair of top and bottom quarks. The data analysed corresponds to 139 fb$^{−1}$ of pp collisions at $\sqrt s$ = 13 TeV recorded by the ATLAS detector at the LHC from 2015 to 2018. The production of a charged Higgs boson in association with a top and a bottom quarks, pp→tbH$^+$→ttbb, is explored in the mass range from m(H$^{\pm}$) = 200 to 2000 GeV using multi-jet final states with one electron or muon. Events are categorised according to the multiplicity of jets and how likely these are to have originated from hadronisation of a bottom quark. A mass-parameterised neural network is used to discriminate between signal and background events and fitted in four separate signal regions.

Keywords: 13 TeV,Charged Higgs searches,BSM Higgs searches,BSM search,c-hadron,b-hadron,Boosted,>=3 jets,2 leptons,1 lepton

31-JUL-2013139 fb-1Documents | Internal
MUONConference noteMuon reconstruction and identification performance in ATLAS using the full Run 2 pp collision data set at 13 TeVFull Title: Muon reconstruction and identification efficiency in ATLAS using the full Run 2 $pp$ collision data set at $\sqrt{s}=13$ TeV

Abstract: This note documents the muon identification performance obtained by the ATLAS experiment between 2015 and 2018 during the LHC Run 2, corresponding to 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV. The increased instantaneous luminosity delivered by the LHC over this period demanded a re-optimization of the criteria for the identification of prompt muons. Improved and newly-developed algorithms were deployed to preserve high muon identification efficiency with a low misidentification rate and good momentum resolution. The availability of statistically large samples of $Z\to\mu\mu$ and $J/\psi\to\mu\mu$ decays, and the minimization of systematic uncertainties, allow for the measurement of the efficiencies of muon identification, association to the primary-vertex, and isolation criteria with accuracy at the per mille level in the bulk of the phase space, and up to the percent level in complex kinematic configurations. Excellent performance is achieved over a range of transverse momenta from 3 GeV to several TeV, and across the full detector acceptance of $|\eta|<2.7$.

Keywords: 13 TeV

30-JUL-2013139 fb-1Documents | Internal
SUSYConference noteSearch for sbottoms with b-jets and hadronic tausFull Title: Search for bottom-squark pair production in $pp$ collision events at $\sqrt{s } = 13$ TeV with hadronically decaying tau leptons, $b$-jets andmissing transverse momentum using the ATLAS detector

Abstract: A search for pair production of bottom squarks in events with hadronically decaying tau leptons, $b$-tagged jets and large missing transverse momentum is presented. The analyzed dataset is based on proton$-$proton collisions at $\sqrt{s}=13$TeV delivered by the Large Hadron Collider and recorded by the ATLAS detector from 2015 to 2018, and corresponds to an integrated luminosity of 139 fb$^{-1}$. The observed data are compatible with the expected Standard Model background. Results are interpreted in a simplified model, where each bottom squark is assumed to decay to the second-lightest neutralino $\tilde \chi_2^0$ and a bottom quark, with $\tilde \chi_2^0$ decaying to a Higgs boson and the lightest neutralino $\tilde \chi_1^0$. The search focusses on final states where at least one Higgs boson decays to a pair of hadronically decaying tau leptons. This allows to significantly improve the acceptance and thus the sensitivity with respect to previous results at low masses of the $\tilde \chi_2^0$, where bottom-squark masses up to 850 GeV are excluded at the 95% confidence level, assuming a mass difference of 130 GeV between $\tilde \chi_2^0$ and $\tilde \chi_1^0$.

Keywords: 13 TeV,Sbottom pair production,BSM search,MET,Taus

30-JUL-2013139 fb-1Documents | Internal
SUSYConference noteChargino-neutralino pair; 4 leptonsFull Title: Search for supersymmetry in events with four or more leptons in 139 fb$^{-1}$ $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

Abstract: A search for supersymmetry in events with four or more charged leptons (electrons, muons and taus) is presented. The analysis uses a data sample corresponding to $139\,\mathrm{fb}^{-1}$ of $pp$ 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 several supersymmetric models, while a general five-lepton signal region targets any new physics phenomena leading to a five charged lepton final state. Data yields are consistent with expectations and results are used to set upper limits on contributions 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 up to $550\,$GeV. In $R$-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of $1.65\,$TeV, $1.23\,$TeV, and $2.58\,$TeV are placed on wino, slepton and gluino masses, respectively.

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

30-JUL-2013139 fb-1Documents | Internal
HDBSPaperBoosted HH to bb tautauFull Title: Reconstruction and identification of boosted di-$\tau$ systems in a search for Higgs boson pairs using 13 TeV proton--proton collision data in ATLAS

Abstract: In this paper, a novel technique, referred to as the di-$\tau$ tagger, is designed to reconstruct and identify hadronically decaying $\tau^+\tau^-$ pairs with a large Lorentz boost in the ATLAS experiment at the Large Hadron Collider. A benchmark di-$\tau$ tagging selection is employed in the search for resonant Higgs boson pair production, where one Higgs boson decays into a boosted $b\bar{b}$ pair and the other into a boosted $\tau^+\tau^-$ pair, with two hadronically decaying $\tau$-leptons in the final state. Using 139 fb$^{-1}$ of proton-proton collision data recorded at a centre-of-mass energy of 13 TeV, the efficiency of the di-$\tau$ tagger is determined and the background with quark- or gluon-initiated jets misidentified as di-$\tau$ objects is estimated. The search for a heavy, narrow, scalar resonance produced via gluon-gluon fusion and decaying into two Higgs bosons is carried out in the mass range 1-3 TeV using the same dataset. No deviations from the Standard Model predictions are observed and 95% confidence-level exclusion limits are set on this model.

Keywords: 13 TeV,Di-Higgs production,Di-Higgs production,Di-Higgs,b-jets,Taus

29-JUL-2013139 fb-1Documents | 2007.14811 | Inspire
HepData | Internal
HIGGConference noteVBF H(125) -> WWFull Title: Observation of vector-boson-fusion production of Higgs bosons in the $H{\rightarrow\,}WW^{\ast}{\rightarrow\,}e\nu\mu\nu$ decay channel in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: An observation of vector-boson-fusion (VBF) production of Higgs bosons in the $H{\rightarrow\,}WW^{\ast}{\rightarrow\,}e\nu\mu\nu$ decay channel is presented. The proton-proton collision data used to obtain this result were produced at the LHC with a center-of-mass energy of 13 TeV and recorded with the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of $\mathrm{139~fb^{-1}}$. The signal is observed (expected) with a significance of 7.0 (6.2) standard deviations. The product of the total VBF cross-section times the ${H{\rightarrow\,}WW^{\ast}}$ branching fraction is measured to be $0.85 \pm 0.10\;(\mathrm{stat.})\;^{+0.17}_{-0.13}\;(\mathrm{syst.})~\mathrm{pb}$, compatible with the Standard Model prediction of $0.81\pm 0.02$ pb.

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

29-JUL-2013139 fb-1Documents | Internal
HIGGConference noteVBF H(125) -> bb (photon-tagged)Full Title: Search for Higgs boson production in association with a high-energy photon in vector boson fusion at $\sqrt{s}= $ 13 TeV with the ATLAS detector

Abstract: A search is presented for the production of the Standard Model Higgs boson in association with a high-energy photon. With a focus on the vector boson fusion process and the dominant Higgs decay to $b$ quark pairs, the search benefits from a large reduction of multijet background compared to more inclusive searches. Results are reported from the analysis of 132 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}= $13 TeV collected with the ATLAS detector at the LHC. The measured Higgs boson signal yield in this final state signature is 1.3$\pm$1.0 times the Standard Model prediction. The observed significance of the Higgs boson signal above the background is 1.3 standard deviations compared to an expected significance of 1.0 standard deviations.

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

29-JUL-2013139 fb-1Documents | Internal
TOPQPaperEvidence for four-top-quarks production in the two same-sign lepton and three lepton channelsFull Title: Evidence for $t\bar{t}t\bar{t}$ production in the multilepton final state in proton-proton collisions at $\sqrt{s}$=13 TeV with the ATLAS detector

Abstract: A search is presented for four-top-quark production using an integrated luminosity of 139 fb$^{-1}$ of proton$-$proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds.The four-top-quark production cross section is measured to be 24$^{+7}_{-6}$ fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process.

Keywords: 13 TeV,ttbar cross-section measurements,Top pair production,MVA / machine learning,Cross-section measurement,>=3 leptons,2 leptons (same charge),2 leptons,1 lepton

29-JUL-2013139 fb-1Documents | 2007.14858 | Inspire
Briefing | Internal
EXOTConference noteSearch for third-generation scalar leptoquarks decaying to a top quark and a tau leptonFull Title: Search for third-generation scalar leptoquarks decaying to a top quark and a $\tau$-lepton in pp collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a tau-lepton is presented. The search is based on a dataset of $pp$ collisions at $\sqrt{s}$ = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$^{-1}$. Events are selected with one light lepton (electron or muon) and at least one hadronically decaying tau-lepton, or at least two light leptons. In addition, two or more jets, at least one of which must be identified as arising from the fragmentation of b-hadrons, are required. Five final states, defined by the multiplicity and flavour of lepton candidates, are considered in the analysis. Each of them is split into multiple event categories to simultaneously search for the signal and constrain several leading backgrounds. The most sensitive event categories require at least one hadronically decaying tau-lepton candidate and exploit the presence of energetic final state objects, which is characteristic of signal events. No significant excess above the Standard Model expectation is observed in any of the considered event categories, and 95% CL upper limits are set on the production cross section as a function of the leptoquark mass, under different assumptions for the branching fractions into $t\tau$ and $b\nu$. Scalar leptoquarks decaying exclusively into $t\tau$ are excluded up to masses of 1.43 TeV while, for a branching fraction of 50% into $t \tau$, the lower mass limit is 1.22 TeV.

Keywords: Taus,13 TeV,Leptoquarks,BSM resonance,BSM search,Top pair,W,b-hadron,Boosted,MET,b-jets,>=3 jets

28-JUL-2013139 fb-1Documents | Internal
HDBSConference noteSearch for heavy resonance decaying to VH in the semileptonic final stateFull Title: Search for heavy resonances decaying into a Z boson and a Higgs boson in final states with leptonsand b-jets with the ATLAS detector

Abstract: This note presents a search for new resonances decaying into a $Z$ boson and a $125~ GeV$ Higgs boson in the $\nu\nu bb$ and $\ell\ell bb$ final states, where $\ell=e^{\pm}$ or $\mu^{\pm}$, in $pp$ collisions at $\sqrt{s}=13~TeV$. The data used correspond to a total integrated luminosity of 139~\ifb\ collected by the ATLAS detector during Run-2 of the Large Hadron Collider. The search is conducted by examining the reconstructed invariant or transverse mass distributions of $Zh$ candidates for evidence of a localised excess in the mass range from $300~{GeV}$ to $5~{TeV}$. No significant excess is observed and $95\%$ confidence level upper limits between 1~pb and 0.4~fb are placed on the production cross-section times branching fraction of $Z^{}$ resonances in heavy-vector-triplet models and the CP-odd scalar boson $A$ in two-Higgs-doublet models.}

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

28-JUL-2013139 fb-1Documents | Internal
HIGGConference noteH(125) combination cross-sections, couplingsFull Title: Combined measurements of Higgs boson production and decay using up to 139 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV collected with the ATLAS experiment

Abstract: A combination of measurements of Higgs boson production cross sections and branching fractions is presented. The combination is based on the analyses of the Higgs boson decay modes $H \to \gamma\gamma$, $ZZ^\ast$, $WW^\ast$, $\tau\tau$, $b\bar{b}$, $\mu\mu$, and searches for decays into invisible final states. Up to $139$~fb$^{-1}$ of proton--proton collision data collected at $\sqrt{s}= 13$ TeV with the ATLAS detector are used. Combined cross section measurements are presented for the gluon--gluon fusion and vector-boson fusion processes, and for associated production with vector bosons or top-quarks. The global signal strength, defined as the measured Higgs boson signal yield normalized to its SM prediction, is determined to be $\mu = 1.06\pm 0.07$. The combined measurement yields an observed (expected) significance for the associated production with a $W$ boson of $6.3\,\sigma$ ($5.2\,\sigma$). Measurements in kinematic regions defined within the simplified template cross section framework are also shown. The results are interpreted in terms of modifiers applied to the Standard Model couplings of the Higgs boson to other particles, and are used to set exclusion limits on parameters in two-Higgs-doublet models. No significant deviations from Standard Model predictions are observed.

Keywords: 13 TeV,kappa,Simplified template cross-section,Coupling measurements,H(125) measurements,BSM reinterpretation,Statistical combination,Cross-section measurement,Higgs

28-JUL-2013139 fb-1Documents | Briefing | Internal
STDMConference noteInclusive four-lepton lepton differential cross sectionsFull Title: Measurement of the four-lepton invariant mass and other differential cross-sections in four-lepton events in 13 TeV proton-proton collisions with the ATLAS detector

Abstract: Measurements of four-lepton differential and integrated fiducial cross-sections in events with two same-flavour, opposite-charge electron or muon pairs are presented. The data correspond to 139~fb$^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collisions, collected by the ATLAS detector during Run 2 of the Large Hadron Collider (2015-2018). The final-state has contributions from a number of interesting Standard Model processes that dominate in different four-lepton invariant mass regions, including single $Z$ boson production, Higgs boson production and on-shell $ZZ$ production, with a complex mix of interference terms, and possible contributions from beyond-the-Standard Model physics. The differential cross-sections include the four-lepton invariant mass inclusively, in slices of other kinematic variables, and in different lepton flavour categories. Also measured are di-lepton invariant masses, transverse momenta, and angular correlation variables, in four regions of four-lepton invariant mass, each dominated by different processes. The measurements are corrected for detector effects and are compared to state-of-the-art Standard Model calculations, which are found to be consistent with the data. The $Z\to 4\ell$ branching fraction is extracted, giving a value of $\left(4.41 \pm 0.30\right) \times 10^{-6}$. Constraints on a model based on a spontaneously broken B-L gauge symmetry are also evaluated.

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

28-JUL-2013139 fb-1Documents | Internal
STDMConference noteMeasurement of the inclusive photon pair production at 13 TeVFull Title: Measurement of the production cross-section of isolated-photon pairs in pp collisions at 13 TeV with the ATLAS detector

Abstract: A measurement of prompt photon-pair production in proton-proton collisions at $\sqrt{s}=13$ TeV is presented. The data were recorded by the ATLAS detector at the LHC with an integrated luminosity of 139 fb$^{-1}$. Events with two photons in the well-instrumented region of the detector are selected, and the photons are required to be isolated and have $E_\mathrm{T,\gamma_{1(2)}} > 40(30)\:$GeV for the two leading photons ordered in transverse energy. The differential cross section as functions of several observables for the diphoton system are measured in the fiducial volume and compared to theoretical predictions from state-of-the-art Monte Carlo and fixed-order calculations. The measured integrated cross section is compatible with the predictions from next-to-next-to-leading order and multileg-merged calculations. Predictions from lower-orders in perturbative QCD fail to agree with data within their estimated theoretical uncertainties. Agreement between measured differential cross sections and the most accurate predictions is generally good where expected, showing a clear necessity to take higher-order perturbative QCD corrections into account.

Keywords: 13 TeV,Jets and photons,Differential measurement,Cross-section measurement,Di-photon,Photon,Photons

28-JUL-2013139 fb-1Documents | Internal
SUSYConference noteSearch for DM and stops in tt2L + MET final statesFull Title: Search for new phenomena in events with two opposite-charge leptons and missing transverse energy in pp collisions at sqrt(s) = 13 TeV with the ATLAS detector

Abstract: The results of a search for direct pair production of top squarks and for dark matter in events with two opposite-charge leptons (electrons or muons), jets and missing transverse momentum are reported, using 139 fb$^{-1}$ of integrated luminosity from proton-proton collisions at $\sqrt{s}=13$ TeV, collected by the ATLAS detector at the Large Hadron Collider during Run-2 (2015-2018). This analysis considers the pair production of top squarks and is sensitive across a wide range of mass differences between the $\tilde{t}$ and lightest neutralino $\tilde{\chi}_{1}^{0}$. Additionally, spin-0 mediator dark matter models are considered, in which the mediator is produced in association with a pair of top quarks. The mediator subsequently decays to a pair of dark-matter particles. No significant excess of events is observed above the Standard Model background, and limits are set at $95\%$ confidence level. The results exclude $\tilde{t}$ masses up to about 1 TeV, and $\tilde{\chi}_{1}^{0}$ masses up to about 500 GeV. Limits on Dark Matter production are set for scalar (pseudoscalar) mediator masses up to about 250~(300) GeV.

Keywords: 13 TeV,Wimp pair with heavy flavour production,Stop pair production,BSM search,Dark matter,Top pair,MET,b-jets,2 leptons

28-JUL-2013139 fb-1Documents | Internal
SUSYConference noteGluino pair, squark pair; 1 leptonFull Title: Search for squarks and gluinos in final states 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 gluino and squark pair production $pp \rightarrow \tilde{q}\tilde{q}$, $pp \rightarrow \tilde{g}\tilde{g}$ decaying via charginos ($\tilde\chi^\pm_1$) to a final state consisting of a $W$ boson, the lightest neutralino ($\tilde\chi^0_1$), and quarks are presented. The signal is characterized by the presence of a single charged lepton from a $W$ boson decay, jets, and missing transverse momentum. The analysis was performed using proton-proton collision data taken at a center-of-mass energy $\sqrt{s}=13$~TeV provided by the Large Hadron Collider and recorded by the ATLAS experiment, corresponding to 139~fb$^{-1}$. No statistically significant excess of events above the Standard Model expectation is found. Limits are set on the direct production of squarks and gluino in the simplified models: masses of $\tilde{g}$ ($\tilde{q}$) up to 2.2 TeV (1.37 TeV) are excluded at 95\% confidence level.

Keywords: 13 TeV,Chargino/neutralino pair production,Gluino pair production,BSM search,MET,1 lepton

28-JUL-2013139 fb-1Documents | Internal
TOPQPaperBR(W->taunu)/BR(W->munu) in e-mu ttbar eventsFull Title: Test of the universality of $\tau$ and $\mu$ lepton couplings in $W$-boson decays from $t\bar{t}$ events with the ATLAS detector

Abstract: The Standard Model of particle physics encapsulates our current best understanding of physics at the smallest scales. A fundamental axiom of this theory is the universality of the couplings of the different generations of leptons to the electroweak gauge bosons. The measurement of the ratio of the rate of decay of $W$ bosons to $\tau$-leptons and muons, $R(\tau/\mu) = B(W \to \tau \nu_\tau)/B(W \to \mu \nu_\mu)$, constitutes an important test of this axiom. A measurement of this quantity with a novel technique using di-leptonic $t\bar{t}$ events is presented based on 139 fb$^{-1}$ of data recorded with the ATLAS detector in proton--proton collisions at $\sqrt{s}=13$ TeV. Muons originating from $W$ bosons and those originating from an intermediate $\tau$-lepton are distinguished using the lifetime of the $\tau$-lepton, through the muon transverse impact parameter, and differences in the muon transverse momentum spectra. The value of $R(\tau/\mu)$ is found to be $0.992 \pm 0.013 [\pm 0.007 (stat) \pm 0.011 (syst)]$ and is in agreement with the hypothesis of universal lepton couplings as postulated in the Standard Model. This is the most precise measurement of this ratio, and the only such measurement from the Large Hadron Collider, to date.

Keywords: 13 TeV,Other top properties,Top properties measurements,2 leptons

28-JUL-2013139 fb-1Documents | 2007.14040 | Inspire
Briefing | Internal
TOPQConference noteMeasurement of ttZ cross sections in Run 2Full Title: Measurement of the fiducial and differential cross-section of a top quark pair in association with a Z boson at 13 TeV with the ATLAS detector

Abstract: Measurements of both the inclusive and differential production cross sections of a top-quark-antiquark pair in association with a $Z$ boson ($t\bar{t}Z$) are presented. The measurements are performed by targeting final states with three or four isolated leptons (electrons or muons) and are based on $\sqrt{s}=13$ TeV proton-proton collision data with an integrated luminosity of 139 fb$^{-1}$, recorded from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. The inclusive cross section is measured to be $\sigma_{t\bar{t}Z } = 1.05 \pm 0.05$ (stat.) $\pm \, 0.09$ (syst.) pb and found to be in agreement with the most precise theoretical prediction. The differential measurements are presented as a function of a number of kinematic variables which probe the kinematics of the $t\bar{t}Z$ system. Both absolute and normalised differential cross-section measurements are performed at particle and parton levels for specific fiducial volumes.

Keywords: 13 TeV,Top properties measurements,ttbar + boson measurements,EFT,Cross-section measurement,>=3 leptons,2 leptons (same charge),2 leptons,1 lepton

28-JUL-2013139 fb-1Documents | Briefing | Internal
EXOTConference noteDark Matter Search in the MET + tW or tJ final stateFull Title: MET+Wt Dark Matter Search

Abstract: This paper presents a search for dark matter in the context of a two-Higgs-doublet model together with an additional pseudo-scalar mediator, which decays to the dark matter particles ($\chi$). Processes where the pseudo-scalar mediator is produced in association with a single top quark are explored for the first time at the LHC. Several final states are considered, including either one or two charged leptons (electrons or muons) and a significant amount of missing transverse momentum. The analysis is based on the data collected with the ATLAS experiment at $\sqrt{s } = 13$ TeV during LHC Run~2 ($2015-2018$), corresponding to an integrated luminosity of 139 fb$^{-1}$. No significant excess is found with respect to Standard Model predictions. The results are expressed as 95% confidence level limits on the parameters of the signal models considered.

Keywords: 1 lepton,Simplified DM model,BSM search,Dark matter,13 TeV,Single top,W,MET,b-jets,2 leptons

26-JUL-2013139 fb-1Documents | Internal
STDMConference noteTransverse energy-energy correlations and alpha_s extractionFull Title: Determination of the strong coupling constant and test of asymptotic freedom from Transverse Energy-Energy Correlations in multijet events at sqrt(s) = 13 TeV with the ATLAS detector

Abstract: Measurements of transverse energy-energy correlations and their associated azimuthal asymmetries in multi-jet events are presented. The analysis is performed using a data sample containing 139 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of $\sqrt{s } = 13$ TeV, collected with the ATLAS detector at the Large Hadron Collider. The measurements are presented in bins of the scalar sum of the transverse momenta of the two leading jets and unfolded to particle level. The unfolded distributions are fitted to next-to-leading-order perturbative QCD calculations. The agreement between data and theory is excellent, allowing a precision test of QCD at large momentum transfers. The strong coupling constant is extracted from these fits at different scale regimes. A global fit to the transverse energy-energy correlations yields a value of $\alpha_{\mathrm{s}}(m_Z) = 0.1196 \pm 0.0004 \ (\mathrm{exp.}) \ ^{+0.0072}_{-0.0105} \ (\mathrm{theo.})$

Keywords: 13 TeV,Jets and photons,Differential measurement,Cross-section measurement,>=3 jets,2 jets

26-JUL-2013139 fb-1Documents | Internal
STDMPaperMeasurement of hadronic event shapes in multijet final statesFull Title: Measurement of hadronic event shapes in multijet final states at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A measurement of event-shape variables in proton$-$proton collisions at large momentum transfer is presented using data collected at $\sqrt{s } = 13$ TeV with the ATLAS detector at the Large Hadron Collider. Six event-shape variables calculated using hadronic jets are studied in inclusive multijet events using data corresponding to an integrated luminosity of 139 fb$^{-1}$. Measurements are performed in bins of jet multiplicity and in different ranges of the scalar sum of the transverse momenta of the two leading jets, reaching scales beyond 2 TeV. These measurements are compared with predictions from Monte Carlo event generators containing leading-order or next-to-leading order matrix elements matched to parton showers simulated to leading-logarithm accuracy. At low jet multiplicities, shape discrepancies between the measurements and the Monte Carlo predictions are observed. At high jet multiplicities, the shapes are better described but discrepancies in the normalisation are observed.

Keywords: 2 jets,Jets and photons,Differential measurement,All hadronic,>=3 jets

24-JUL-2013139 fb-1Documents | 2007.12600 | Inspire
Internal
TRIGPaperOperation of the ATLAS Trigger SystemFull Title: Operation of the ATLAS trigger system in Run 2

Abstract: The ATLAS experiment at the Large Hadron Collider employs a two-level trigger system to record data at an average rate of 1 kHz from physics collisions, starting from an initial bunch crossing rate of 40 MHz. During the LHC Run 2 (2015$-$2018), the ATLAS trigger system operated successfully with excellent performance and flexibility by adapting to the various run conditions encountered and has been vital for the ATLAS Run-2 physics programme. For proton$-$proton running, approximately 1500 individual event selections were included in a trigger menu which specified the physics signatures and selection algorithms used for the data-taking, and the allocated event rate and bandwidth. The trigger menu must reflect the physics goals for a given data collection period, taking into account the instantaneous luminosity of the LHC and limitations from the ATLAS detector readout, online processing farm, and offline storage. This document discusses the operation of the ATLAS trigger system during the nominal proton$-$proton data collection in Run 2 with examples of special data-taking runs. Aspects of software validation, evolution of the trigger selection algorithms during Run 2, monitoring of the trigger system and data quality as well as trigger configuration are presented.

Keywords: 13 TeV,Trigger operation,Trigger monitoring

24-JUL-2013139 fb-1Documents | 2007.12539 | Inspire
Internal
HIGGPaperSearch H(125)->mumuFull Title: A search for the dimuon decay of the Standard Model Higgs boson with the ATLAS detector

Abstract: A search for the dimuon decay of the Standard Model (SM) Higgs boson is performed using data corresponding to an integrated luminosity of 139 fb$^{-1}$ collected with the ATLAS detector in Run2 $pp$ collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider. The observed (expected) significance over the background-only hypothesis for a Higgs boson with a mass of 125.09 GeV is $2.0\sigma$ ($1.7\sigma$). The observed upper limit on the cross section times branching ratio for $pp \to H \to \mu\mu$ is 2.2 times the SM prediction at 95% confidence level, while the expected limit on a $H \to \mu\mu$ signal assuming the absence (presence) of a SM signal is $1.1$ ($2.0$). The best-fit value of the signal strength parameter, defined as the ratio of the observed signal yield to the one expected in the SM, is $\mu = 1.2 \pm 0.6$.

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

15-JUL-2013139 fb-1Documents | 2007.07830 | Inspire
Briefing | Internal
IDTRPaperAlignment of the ATLAS Inner DetectorFull Title: Alignment of the ATLAS Inner Detector in Run-2

Abstract: The performance of the ATLAS Inner Detector alignment has been studied using $pp$ collision data at $\sqrt{s } = 13$ TeV collected by the ATLAS experiment during Run 2 (2015 to 2018) of the Large Hadron Collider (LHC). The goal of the detector alignment is to determine the detector geometry as accurately as possible and correct for time-dependent movements. The Inner Detector alignment is based on the minimization of track-hit residuals in a sequence of hierarchical levels, from global mechanical assembly structures to local sensors. Subsequent levels have increasing numbers of degrees of freedom; in total there are almost 750000. The alignment determines detector geometry on both short and long timescales, where short timescales describe movements within an LHC fill. The performance and possible track parameter biases originating from systematic detector deformations are evaluated. Momentum biases are studied using resonances decaying to muons or to electrons. The residual sagitta bias and momentum scale bias after alignment are reduced to less than $\sim$ 0.1 TeV$^{-1}$ and 0.9$\times10^{-3}$, respectively. Impact parameter biases are also evaluated using tracks within jets.

Keywords: Track-based alignment

15-JUL-2013139 fb-1Documents | 2007.07624 | Inspire
Internal
TOPQPaperMeasurements of combined ttgamma + tWgamma production cross-sections in the emu channelFull Title: Measurements of inclusive and differential cross-sections of combined $t\bar{t}\gamma$ and $tW\gamma$ production in the $e\mkern-2mu\mu$ channel at 13 TeV with the ATLAS detector

Abstract: Inclusive and differential cross-sections for the production of top quarks in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 139 fb$^{-1}$. The data were collected by the ATLAS detector at the LHC during Run 2 between 2015 and 2018 at a centre-of-mass energy of 13 TeV. The measurements are performed in a fiducial volume defined at parton level. Events with exactly one photon, one electron and one muon of opposite sign, and at least two jets, of which at least one is $b$-tagged, are selected. The fiducial cross-section is measured to be $39.6^{+2.7}_{-2.3}$ fb. Differential cross-sections as functions of several observables are compared with state-of-the-art Monte Carlo simulations and next-to-leading-order theoretical calculations. These include cross-sections as functions of photon kinematic variables, angular variables related to the photon and the leptons, and angular separations between the two leptons in the event. All measurements are in agreement with the predictions from the Standard Model.

Keywords: 13 TeV,ttbar + boson measurements,Differential measurement,Cross-section measurement,Top pair,Photon,2 jets,Photons,2 leptons

14-JUL-2013139 fb-1Documents | 2007.06946 | Inspire
Internal
HDBSPaperVH all hadronic resonance searchFull Title: Search for resonances decaying into a weak vector boson and a Higgs boson in the fully hadronic final state produced in proton$-$proton collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for heavy resonances decaying into a $W$ or $Z$ boson and a Higgs boson produced in proton-proton collisions at the Large Hadron Collider at $\sqrt{s } = 13$ TeV is presented. The analysis utilizes the dominant $W \to q \bar{q}^\prime$ or $Z \to q \bar{q}$ and $H \to b \bar{b}$ decays with substructure techniques applied to large-radius jets. A sample corresponding to an integrated luminosity of 139 fb$^{-1}$ collected with the ATLAS detector is analyzed and no significant excess of data is observed over the background prediction. The results are interpreted in the context of the Heavy Vector Triplet model with spin-1 $W^\prime$ and $Z^\prime$ bosons. Upper limits on the cross section are set for resonances with mass between 1.5 and 5.0 TeV, ranging from 6.8 to 0.53 fb for $W^\prime \to WH$ and from 8.7 to 0.53 fb for $Z^\prime \to ZH$ at the 95% confidence level.

Keywords: 13 TeV,Heavy vector triplets,BSM resonance,Heavy vector triplets,BSM resonance,BSM search,VH,Boosted,All hadronic,2 jets,0 lepton

10-JUL-2013139 fb-1Documents | 2007.05293 | Inspire
HepData | Internal
HIGGPaperVH(125) H->bb STXSFull Title: Measurements of $WH$ and $ZH$ production in the $H \rightarrow b\bar{b}$ decay channel in $pp$ collisions at 13 TeV with the ATLAS detector

Abstract: Measurements of the Standard Model Higgs boson decaying into a $b\bar{b}$ pair and produced in association with a $W$ or $Z$ boson decaying into leptons, using proton-proton collision data collected between 2015 and 2018 by the ATLAS detector, are presented. The measurements use collisions produced by the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s } = $13 TeV, corresponding to an integrated luminosity of 139 fb$^{-1}$. The production of a Higgs boson in association with a $W$ or $Z$ boson is established with observed (expected) significances of 4.0 (4.1) and 5.3 (5.1) standard deviations, respectively. Cross-sections of associated production of a Higgs boson decaying into bottom quark pairs with an electroweak gauge boson, $W$ or $Z$, decaying into leptons are measured as a function of the gauge boson transverse momentum in kinematic fiducial volumes. The cross-section measurements are all consistent with the Standard Model expectations, and the total uncertainties vary from 30% in the high gauge boson transverse momentum regions to 85% in the low regions. Limits are subsequently set on the parameters of an effective Lagrangian sensitive to modifications of the $WH$ and $ZH$ processes as well as the Higgs boson decay into $b\bar{b}$.

Keywords: 13 TeV,Simplified template cross-section,Coupling measurements,H(125) measurements,VH production,Higgs to bb,Cross-section measurement,Higgs,VH,MET,b-jets,2 leptons,1 lepton,0 lepton

06-JUL-2013139 fb-1Documents | 2007.02873 | Inspire
HepData | Briefing | Internal
STDMPaperEW Zjj differential cross sectionsFull Title: Differential cross-section measurements for the electroweak production of dijets in association with a $Z$ boson in proton-proton collisions at ATLAS

Abstract: Differential cross-section measurements are presented for the electroweak production of two jets in association with a $Z$ boson. These measurements are sensitive to the vector-boson fusion production mechanism and provide a fundamental test of the gauge structure of the Standard Model. The analysis is performed using proton$-$proton collision data collected by ATLAS at $\sqrt{s}$=13 TeV and with an integrated luminosity of 139 fb$^{-1}$. The differential cross-sections are measured in the $Z\rightarrow \ell^+\ell^-$ decay channel ($\ell=e,\mu$) as a function of four observables: the dijet invariant mass, the rapidity interval spanned by the two jets, the signed azimuthal angle between the two jets, and the transverse momentum of the dilepton pair. The data are corrected for the effects of detector inefficiency and resolution and are sufficiently precise to distinguish between different state-of-the-art theoretical predictions calculated using Powheg+Pythia8, Herwig7+Vbfnlo and Sherpa 2.2. The differential cross-sections are used to search for anomalous weak-boson self-interactions using a dimension-six effective field theory. The measurement of the signed azimuthal angle between the two jets is found to be particularly sensitive to the interference between the Standard Model and dimension-six scattering amplitudes and provides a direct test of charge-conjugation and parity invariance in the weak-boson self-interactions.

Keywords: Differential measurement,VBF measurements,Electroweak processes,EFT,VBF

27-JUN-2013139 fb-1Documents | 2006.15458 | Inspire
Internal
TOPQPaperMeasurement of the ttbar production cross-section in the lepton+jets channel at 13 TeVFull Title: Measurement of the $t\bar{t}$ production cross-section in the lepton+jets channel at $\sqrt{s}=13\;$!TeV with the ATLAS experiment

Abstract: The $t\bar{t}$ production cross-section is measured in the lepton+jets channel using proton$-$proton collision data at a centre-of-mass energy of $\sqrt{s}$=13 TeV collected with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 139 fb$^{-1}$. Events with exactly one charged lepton and four or more jets in the final state, with at least one jet containing $b$-hadrons, are used to determine the $t\bar{t}$ production cross-section through a profile-likelihood fit. The inclusive cross-section is measured to be $\sigma_{inc} $= 830 $\pm $ 0.4 (stat.) $\pm $ 36 (syst.) $\pm $14 (lumi.) pb with a relative uncertainty of 4.6 %. The result is consistent with theoretical calculations at next-to-next-to-leading order in perturbative QCD.

Keywords: 13 TeV,Lepton-jets,ttbar cross-section measurements,Top pair production,Cross-section measurement,Top pair,b-jets,>=3 jets,1 lepton

24-JUN-2013139 fb-1Documents | 2006.13076 | Inspire
HepData | Internal
EXOTPaperNon-resonant dilepton searchFull Title: Search for new non-resonant phenomena in high-mass dilepton final states with the ATLAS detector

Abstract: A search for new physics with non-resonant signals in dielectron and dimuon final states in the mass range above 2 TeV is presented. This is the first search for non-resonant signals in dilepton final states at the LHC to use a background estimate from the data. The data, corresponding to an integrated luminosity of 139 fb$^{-1}$, were recorded by the ATLAS experiment in proton$-$proton collisions at a centre-of-mass energy of $\sqrt{s } = 13$ TeV during Run 2 of the Large Hadron Collider. The benchmark signal signature is a two-quark and two-lepton contact interaction, which would enhance the dilepton event rate at the TeV mass scale. To model the contribution from background processes a functional form is fit to the dilepton invariant-mass spectra in data in a mass region below the region of interest. It is then extrapolated to a high-mass signal region to obtain the expected background there. No significant deviation from the expected background is observed in the data. Upper limits at 95% CL on the number of events and the visible cross-section times branching fraction for processes involving new physics are provided. Observed (expected) 95% CL lower limits on the contact interaction energy scale reach 35.8(37.6) TeV.

Keywords: 13 TeV,Contact interactions,BSM search,2 leptons

23-JUN-2013139 fb-1Documents | 2006.12946 | Inspire
HepData | Internal
EXOTPaperSearch for leptoquark pairs with 1st/2nd generation leptons and light, c or b quarksFull Title: Search for pairs of scalar leptoquarks decaying into quarks and electrons or muons in $\sqrt{s}=13$ TeV pp collisions with the ATLAS detector

Abstract: A search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented. Scalar leptoquarks pair-produced in pp collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider are considered using an integrated luminosity of 139 fb$^{-1}$, corresponding to the full Run 2 dataset. They are searched for in events with two electrons or two muons and two or more jets, including jets identified as arising from the fragmentation of $c$- or $b$-quarks. The observed yield in each channel is consistent with the Standard Model background expectation. Leptoquarks with masses below 1.8 TeV and 1.7 TeV are excluded in the electron and muon channels, respectively, assuming a branching ratio into a charged lepton and a quark of 100%, with minimal dependence on the quark flavour. Upper limits on the aforementioned branching ratio are also given as a function of the leptoquark mass.

Keywords: 13 TeV,Leptoquarks,BSM resonance,BSM search,b-jets,c-jets,2 jets,2 leptons

10-JUN-2013139 fb-1Documents | 2006.05872 | Inspire
HepData | Internal
SUSYPaperSearch for stop pair production decaying through Z/h bosonsFull Title: Search for top squarks in events with a Higgs or $Z$ boson using 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This paper presents a search for direct top squark pair production in events with missing transverse momentum plus either a pair of jets consistent with Standard Model Higgs boson decay into $b$-quarks or a same-flavour opposite-sign dilepton pair with an invariant mass consistent with a $Z$ boson. The analysis is performed using the proton$-$proton collision data at $\sqrt{s}=13$ TeV collected with the ATLAS detector during the LHC Run-2, corresponding to an integrated luminosity of 139 fb$^{-1}$. No excess is observed in the data above the Standard Model predictions. The results are interpreted in simplified models featuring direct production of pairs of either the lighter top squark ($\tilde{t}_1$) or the heavier top squark ($\tilde{t}_2$), excluding at 95% confidence level $\tilde{t}_1$ and $\tilde{t}_2$ masses up to about 1220 and 875 GeV, respectively.

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

10-JUN-2013139 fb-1Documents | 2006.05880 | Inspire
Internal
EXOTConference notePhoton + MET Search Full Title: Search for dark matter in association with an energetic photon in pp collisions at $\sqrt(s) = 13$ TeV with the ATLAS detector

Abstract: A search for dark matter is conducted in final states containing a photon and missing transverse momentum in proton-proton collisions at 13 TeV. The data, collected during 2015-2018 by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb-1. No deviations are observed relative to the predictions of the Standard Model. The results are interpreted as exclusion limits in models where weakly interacting dark-matter candidates are pair-produced via an axial-vector or a vector mediator in the s-channel. Results are also expressed in terms of 95% confidence level limits on the parameters of a model with an axion-like particle produced in association with a photon.

Keywords: 13 TeV,BSM search,ISR,Dark matter,MET,Photons,0 lepton

02-JUN-2013139 fb-1Documents | Internal
SUSYConference noteSearch for chargino-neutralino pairs in 3L final statesFull Title: Search for chargino-neutralino pair production in final states with three leptons and missing transverse momentum in $\sqrt{s } = 13$ TeV$pp$ collisions with the ATLAS detector

Abstract: A search for chargino-neutralino pair production in three-lepton final states with missing transverse momentum in $\sqrt{s}$ = 13 TeV p-p collisions with the ATLAS detector is presented. Strategies targeting decays with intermediate $W$, $Z$ bosons or intermediate $W$, Higgs ($h$) bosons are discussed. The search targets a model in which the chargino ($\tilde{\chi}^{\pm}_{1}$) and next-to-lightest neutralino ($\tilde{\chi}^{0}_{2}$) are mass degenerate. The $\tilde{\chi}^{\pm}_{1}$ decays to a lightest neutralino ($\tilde{\chi}^{0}_{1}$) and a $W$ boson, while the $\tilde{\chi}^{0}_{2}$ decays to a $\tilde{\chi}^{0}_{1}$ and a $Z$ or Higgs ($h$) boson. Only leptonic decays of the Standard Model bosons are considered. Strategies targeting scenarios where the mass difference between the $\tilde{\chi}^{\pm}_{1}$/$\tilde{\chi}^{0}_{2}$ and $\tilde{\chi}^{0}_{1}$ is above the $Z$-boson mass, with on-shell $W$ and $Z$ bosons or on-shell $W$ and $h$ bosons, and scenarios where the mass difference is between 10-90 GeV, with off-shell $W^{*}$ and $Z^{*}$ bosons, are discussed. A dataset corresponding to an integrated luminosity of 139 fb$^{-1}$ is used and no significant excess is found in data with respect to the Standard Model predictions. Exclusion limits at 95% confidence level are set on a simplified model of pure wino $\tilde{\chi}^{\pm}_{1}\tilde{\chi}^{0}_{2}$ pair production. Models with $\tilde{\chi}^{\pm}_{1}$ and $\tilde{\chi}^{0}_{2}$ are excluded up to 640 GeV for decays via on-shell $W$ and $Z$ bosons and massless $\tilde{\chi}^{0}_{1}$, up to 300 GeV for decays via off-shell $W^{*}$ and $Z^{*}$ bosons, and up to 185 GeV for on-shell $W$ and $h$ bosons and $\tilde{\chi}^{0}_{1}$ masses less than 20 GeV.

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

24-MAY-2013139 fb-1Documents | Internal
TRIGPaperRun-2 MET trigger performanceFull Title: Performance of the missing transverse momentum triggers for the ATLAS detector during Run-2 data taking

Abstract: The factor of four increase in the LHC luminosity, from $0.5\times 10^{34}\,\textrm{cm}^{-2}\textrm{s}^{-1}$ to $2.0\times 10^{34}\textrm{cm}^{-2}\textrm{s}^{-1}$, and the corresponding increase in pile-up collisions during the 2015-2018 data-taking period, presented a challenge for ATLAS to trigger on missing transverse momentum. The output data rate at fixed threshold typically increases exponentially with the number of pile-up collisions, so the legacy algorithms from previous LHC data-taking periods had to be tuned and new approaches developed to maintain the high trigger efficiency achieved in earlier operations. A study of the trigger performance and comparisons with simulations show that these changes resulted in event selection efficiencies of $>98 for this period, meeting and in some cases exceeding the performance of similar triggers in earlier run periods, while at the same time keeping the necessary bandwidth within acceptable limits.

Keywords: MET,Missing transverse energy trigger

19-MAY-2013139 fb-1Documents | 2005.09554 | Inspire
Internal
EXOTPaperSearch for high-mass ttbar resonances hadronicFull Title: Search for $t\bar{t}$ resonances in fully hadronic final states in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This paper presents a search for new heavy particles decaying into a pair of top quarks using 139 fb$^{-1}$ of proton$-$proton collision data recorded at a centre-of-mass energy of $\sqrt{s}=13$ TeV with the ATLAS detector at the Large Hadron Collider. The search is performed using events consistent with pair production of high-transverse-momentum top quarks and their subsequent decays into the fully hadronic final states. The analysis is optimized for resonances decaying into a $t\bar{t}$ pair with mass above 1.4 TeV, exploiting a dedicated multivariate technique with jet substructure to identify hadronically decaying top quarks using large-radius jets and evaluating the background expectation from data. No significant deviation from the background prediction is observed. Limits are set on the production cross-section times branching fraction for the new $Z$ boson in a topcolor-assisted-technicolor model. The $Z$ boson masses below 3.9 and 4.7 TeV are excluded at 95% confidence level for the decay widths of 1% and 3%, respectively.

Keywords: 13 TeV,Other new particle searches,BSM resonance,MVA / machine learning,BSM search,Top pair,Boosted,b-jets,All hadronic,2 jets,0 lepton

11-MAY-2013139 fb-1Documents | 2005.05138 | Inspire
HepData | Internal
HIGGPaperH(125) -> ZgammaFull Title: A search for the $Z\gamma$ decay mode of the Higgs boson in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for the $Z\gamma$ decay of the Higgs boson, with $Z$ boson decays into pairs of electrons or muons is presented. The analysis uses proton$-$proton collision data at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS detector at the Large Hadron Collider. The observed data are consistent with the expected background with a $p$-value of 1.3%. An upper limit at 95% confidence level on the production cross-section times the branching ratio for $pp\to H\to Z\gamma$ is set at 3.6 times the Standard Model prediction while 2.6 times is expected in the presence of the Standard Model Higgs boson. The best-fit value for the signal yield normalised to the Standard Model prediction is $2.0^{+1.0}_{-0.9}$ where the statistical component of the uncertainty is dominant.

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

11-MAY-2013139 fb-1Documents | 2005.05382 | Inspire
HepData | Briefing | Internal
TDAQPaperPerformance of L1Calo nMCM in Run2Full Title: Performance of the upgraded PreProcessor of the ATLAS Level-1 Calorimeter Trigger

Abstract: The PreProcessor of the ATLAS Level-1 Calorimeter Trigger prepares the analogue trigger signals sent from the ATLAS calorimeters by digitising, synchronising and calibrating them to reconstruct transverse energy deposits, which are then used in further processing to identify event features. During the first long shutdown of the LHC from 2013 to 2014, the central components of the PreProcessor, the Multichip Modules, were replaced by upgraded versions that feature modern ADC and FPGA technology in order to ensure optimal performance in the high pile-up environment of LHC Run 2. This paper describes the new Multichip Modules and the achieved improvements to the signal processing.

Keywords: Charged tracks,Trigger-level objects,Level-1 calorimeter trigger

08-MAY-2013139 fb-1Documents | 2005.04179 | Inspire
Internal
HDBSPaperDijet Resonance Search using Weak SupervisionFull Title: Dijet resonance search with weak supervision using $\sqrt{s}=13$ TeV $pp$ collisions in the ATLAS detector

Abstract: This Letter describes a search for resonant new physics using a machine-learning anomaly detection procedure that does not rely on a signal model hypothesis. Weakly supervised learning is used to train classifiers directly on data to enhance potential signals. The targeted topology is dijet events and the features used for machine learning are the masses of the two jets. The resulting analysis is essentially a three-dimensional search $A\rightarrow BC$, for $m_A\sim\mathcal{O}(\text{TeV})$, $m_B,m_C\sim\mathcal{O}(100\text{ GeV})$ and $B,C$ are reconstructed as large-radius jets, without paying a penalty associated with a large trials factor in the scan of the masses of the two jets. The full Run 2 $\sqrt{s}=13$ TeV $pp$ collision data set of 139 fb$^{-1}$ recorded by the ATLAS detector at the Large Hadron Collider is used for the search. There is no significant evidence of a localized excess in the dijet invariant mass spectrum between 1.8 and 8.2 TeV. Cross-section limits for narrow-width $A$, $B$, and $C$ particles vary with $m_A$, $m_B$, and $m_C$. For example, when $m_A=3$ TeV and $m_B\gtrsim 200$ GeV, a production cross section between 1 and 5 fb is excluded at 95% confidence level, depending on $m_C$. For certain masses, these limits are up to 10 times more sensitive than those obtained by the inclusive dijet search.

Keywords: BSM Higgs searches

06-MAY-2013139 fb-1Documents | 2005.02983 | Inspire
Internal
HDBSPaperSearch for heavy resonances decaying to VV in the semileptonic final statesFull Title: Search for heavy diboson resonances in semileptonic final states in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: This paper reports on a search for heavy resonances decaying into $WW$, $ZZ$ or $WZ$ using proton-proton collision data at a centre-of-mass energy of $\sqrt{s}=13$ TeV. The data, corresponding to an integrated luminosity of 139 $\mathrm{fb^{-1}}$, were recorded with the ATLAS detector from 2015 to 2018 at the Large Hadron Collider. The search is performed for final states in which one $W$ or $Z$ boson decays leptonically, and the other $W$ boson or $Z$ boson decays hadronically. The data are found to be described well by expected backgrounds. Upper bounds on the production cross sections of heavy scalar, vector or tensor resonances are derived in the mass range 300-5000 GeV within the context of Standard Model extensions with warped extra dimensions or including a heavy vector triplet. 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,Heavy vector triplets,BSM resonance,BSM search,VBF,Gluon fusion,ZZ,WZ,WW,Boosted,MET,b-jets,>=3 jets,2 jets,1 jet,2 leptons,1 lepton,0 lepton

30-APR-2013139 fb-1Documents | 2004.14636 | Inspire
HepData | Internal
SUSYPaperStop pair; 0 lepton; leptoquarksFull Title: Search for a scalar partner of the top quark in the all-hadronic $t\bar{t}$ plus missing transverse momentum final state at $\sqrt{s}$=13 TeV with the ATLAS detector

Abstract: A search for direct pair production of scalar partners of the top quark (top squarks or scalar third-generation up-type leptoquarks) in the all-hadronic $t\bar{t}$ plus missing transverse momentum final state is presented. The analysis of 139 fb$^{-1}$ of $\sqrt{s}$=13 TeV proton$-$proton collision data collected using the ATLAS detector at the LHC yields no significant excess over the Standard Model background expectation. To interpret the results, a supersymmetric model is used where the top squark decays via $\tilde{t} \to t^{( * )} \tilde{\chi}^0_1$, with $t^{( * )}$ denoting an on-shell (off-shell) top quark and $\tilde{\chi}^0_1$ the lightest neutralino. Three specific event selections are optimised for the following scenarios. In the scenario where $m_{\tilde{t}}> m_t+m_{\tilde{\chi}^0_1}$, top squark masses are excluded in the range 400-1250 GeV for $\tilde{\chi}^0_1$ masses below 200 GeV at 95% confidence level. In the situation where $m_{\tilde{t}}\sim m_t+m_{\tilde{\chi}^0_1}$, top squark masses in the range 300-630 GeV are excluded, while in the case where $m_{\tilde{t}}< m_W+m_b+m_{\tilde{\chi}^0_1}$ (with $m_{\tilde{t}}-m_{\tilde{\chi}^0_1}\ge$ 5 GeV), considered for the first time in an ATLAS all-hadronic search, top squark masses in the range 300-660 GeV are excluded. Limits are also set for scalar third-generation up-type leptoquarks, excluding leptoquarks with masses below 1240 GeV when considering only leptoquark decays into a top quark and a neutrino.

Keywords: 13 TeV,Leptoquarks,Stop pair production,BSM search,Dark matter,Top pair,MET,b-jets,All hadronic,0 lepton

29-APR-2013139 fb-1Documents | 2004.14060 | Inspire
HepData | Internal
TRIGPaperMuon trigger performance in Run 2Full Title: Performance of the ATLAS muon triggers in Run 2

Abstract: The performance of the ATLAS muon trigger system is evaluated with proton$-$proton ($pp$) and heavy-ion (HI) collision data collected in Run 2 during 2015-2018 at the Large Hadron Collider. It is primarily evaluated using events containing a pair of muons from the decay of $Z$ bosons to cover the intermediate momentum range between 25 GeV and 100 GeV. Overall, the efficiency of the single-muon triggers is about 68 % in the barrel region and 85% in the endcap region. The $p_\mathrm{T}$ range for efficiency determination is extended by using muons from decays of $J/\psi$ mesons, $W$ bosons, and top quarks. The performance in HI collision data is measured and shows good agreement with the results obtained in $pp$ collisions. The muon trigger shows uniform and stable performance in good agreement with the prediction of a detailed simulation. Dedicated multi-muon triggers with kinematic selections provide the backbone to beauty, quarkonia, and low-mass physics studies. The design, evolution and performance of these triggers are discussed in detail.

Keywords: 13 TeV,Muon trigger

28-APR-2013139 fb-1Documents | 2004.13447 | Inspire
Internal
SUSYPaperChargino-neutralino pair; Higgs boson in final state, 2 photonsFull Title: Search for direct production of electroweakinos in final states with missing transverse momentum and a Higgs boson decaying into photons in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for a chargino$-$neutralino pair decaying via the 125 GeV Higgs boson into photons is presented. The study is based on the data collected between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 139 fb$^{-1}$ of $pp$ collisions at a centre-of-mass energy of 13 TeV. No significant excess over the expected background is observed. Upper limits at 95% confidence level for a massless $\tilde{\chi}^{0}_{1}$ are set on several electroweakino production cross-sections and the visible cross-section for beyond the Standard Model processes. In the context of simplified supersymmetric models, 95% confidence-level limits of up to 310 GeV in $m(\tilde{\chi}^{\pm}_{1}/\tilde{\chi}^{0}_{2})$, where $m(\tilde{\chi}^{0}_{1}) = 0.5$ GeV, are set. Limits at 95% confidence level are also set on the $\tilde{\chi}^{\pm}_{1}\tilde{\chi}^{0}_{2}$ cross-section in the mass plane of $m(\tilde{\chi}^{\pm}_{1}/\tilde{\chi}^{0}_{2})$ and $m(\tilde{\chi}^{0}_{1})$, and on scenarios with gravitino as the lightest supersymmetric particle. Upper limits at the 95% confidence-level are set on the higgsino production cross-section. Higgsino masses below 380 GeV are excluded for the case of the higgsino fully decaying into a Higgs boson and a gravitino.

Keywords: 13 TeV,Chargino/neutralino pair production,BSM search,Higgs,Di-photon,W,MET,Photons,1 lepton

23-APR-2013139 fb-1Documents | 2004.10894 | Inspire
Internal
STDMPaperObservation of electroweak ZZjj productionFull Title: Observation of electroweak production of two jets and a $Z$-boson pair with the ATLAS detector at the LHC

Abstract: Electroweak symmetry breaking explains the origin of the masses of elementary particles via their interactions with the Higgs field. Besides the measurements of the Higgs boson properties, the study of the scattering of massive vector bosons (with spin one) at the Large Hadron Collider allows to probe the nature of electroweak symmetry breaking with an unprecedented sensitivity. Among all processes related to vector-boson scattering, the electroweak production of two jets and a $Z$-boson pair is a rare and important one. This article reports on the first observation of this process using proton-proton collision data corresponding to an integrated luminosity of 139 fb$^{-1}$ recorded at a centre-of-mass energy of 13 TeV by the ATLAS detector. Two different final states originating from the decays of the $Z$-boson pair, one containing four charged leptons and the other containing two charged leptons and two neutrinos, are considered. The hypothesis of no electroweak production is rejected with a statistical significance of 5.5 $\sigma$, and the measured cross-section for electroweak production is consistent with the Standard Model prediction. In addition, cross-sections for inclusive production of a $Z$-boson pair and two jets are reported for the two final states.

Keywords: 13 TeV,VBS measurements,Electroweak processes,VBS,ZZ,MET,2 jets,>=3 leptons,2 leptons

22-APR-2013139 fb-1Documents | 2004.10612 | Inspire
HepData | Internal
SUSYConference noteSearch for chargino and neutralino pair RPV decays; 3LFull Title: Search for trilepton resonances from chargino and neutralino pair production in $\sqrt{s } = 13$ TeV $pp$ collisions with the ATLAS detector

Abstract: A search is performed for the electroweak pair production of charginos and neutralinos which each decay through an R-parity-violating coupling to a lepton and a $W$, $Z$, or Higgs boson. The trilepton invariant mass spectrum is constructed from events with three or more leptons, targeting chargino decays that include an electron or muon and a leptonically-decaying Z boson. The analyzed dataset corresponds to an integrated luminosity of 139 fb$^{-1}$ of proton-proton collision data produced by the Large Hadron Collider at a center-of-mass energy of $\sqrt{s}$ = 13 TeV and collected by the ATLAS experiment between 2015 and 2018. The data are found to be consistent with predictions from the Standard Model. The results are interpreted as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model. Limits are also set on the production of charginos and neutralinos for a Minimal Supersymmetric Standard Model with an approximate B-L symmetry. Charginos and neutralinos with masses between 100 GeV and 1050 GeV are excluded for various assumptions on the decay branching fractions into electron, muon, or $\tau$ leptons and into $W$, $Z$, or Higgs bosons.

Keywords: 13 TeV,RPV SUSY,Chargino/neutralino pair production,BSM search,Z,>=3 leptons

17-APR-2013139 fb-1Documents | Briefing | Internal
HIGGPaperttH(125) H->gammagamma CP studiesFull Title: Study of the CP properties of the interaction of the Higgs boson with top quarksy using top quark associated production of the Higgs boson and its decay into two photons with the ATLAS detector at the LHC

Abstract: A study of the CP properties of the interaction between the Higgs boson and top quarks is presented. Higgs bosons are identified via the diphoton decay channel ($H \rightarrow \gamma\gamma$) and their production in association with a top quark pair ($t\bar{t}H$) or single top quark ($tH$) is studied. The analysis uses 139 fb$^{-1}$ of proton$-$proton collision data recorded at a center-of-mass energy of $\sqrt{s}$ = 13 TeV with the ATLAS detector at the Large Hadron Collider. It is performed using a fit to the diphoton invariant mass $m_{\gamma\gamma}$ distribution in events categorized using two independent boosted decision trees. Twelve categories are used for events where top quarks decay hadronically and eight for events where at least one top quark decays leptonically. Assuming a CP-even coupling, the $t\bar{t}H$ process is observed with a significance of 5.2 standard deviations. The $tH$ production process is not observed and an upper limit on its rate of 12 times the Standard Model expectation is set. A CP-mixing angle greater than $43^\circ$ is excluded at 95% confidence level.

Keywords: 13 TeV,Spin / CP,H(125) measurements,ttH production,Higgs to 2 photons,Higgs,Top pair,Di-photon,b-jets,Photons

09-APR-2013139 fb-1Documents | 2004.04545 | Inspire
Briefing | Internal
EXOTConference noteSearch for invisible Higgs decays in VBF + MET eventsFull Title: Search for invisible Higgs boson decays with vector boson fusion signatures with the ATLAS detector using an integrated luminosity of 139 fb$^{-1}$

Abstract: A direct search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles is reported.The analysis uses 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 13 TeV recorded by the ATLAS detector at the LHC. The observed number of events are found to be in agreement with the background expectation from Standard Model processes. Assuming a 125 GeV scalar Higgs boson with a Standard Model production cross section, both the observed and expected upper limits on the branching fraction of its decay into invisible particles are derived to be 0.13 at 95$\%$ confidence level. These results are also interpreted in the context of models where the 125 GeV Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross-section of weakly interacting massive particles and nucleons. The invisible decays of additional scalar bosons with masses from 50 GeV up to 1 TeV are also studied, and upper limits on the cross section times branching fraction are evaluated to be 0.97 pb for a scalar boson mass of 50 GeV, which falls with increasing mass to become 0.12 pb at a mass of 1 TeV.

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

08-APR-2013139 fb-1Documents | Briefing | Internal
HIGGPaperH(125)->4l differential cross sectionsFull Title: Measurements of the Higgs boson inclusive and differential fiducial cross sections in the 4$\ell$ decay channel at $\sqrt{s}$ = 13 TeV

Abstract: Inclusive and differential fiducial cross sections of the Higgs boson are measured in the $H \to ZZ^{*} \to 4\ell$ ($\ell = e,\mu$) decay channel. The results are based on proton$-$proton collision data produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector from 2015 to 2018, equivalent to an integrated luminosity of 139 fb$^{-1}$. The inclusive fiducial cross section for the $H \to ZZ^{*} \to 4\ell$ process is measured to be $\sigma_\mathrm{fid } = 3.28 \pm 0.32$ fb, in agreement with the Standard Model prediction of $\sigma_\mathrm{fid, SM } = 3.41 \pm 0.18 $ fb. Differential fiducial cross sections are measured for a variety of observables which are sensitive to the production and decay of the Higgs boson. All measurements are in agreement with the Standard Model predictions. The results are used to constrain anomalous Higgs boson interactions with Standard Model particles.

Keywords: 13 TeV,H(125) measurements,Higgs to ZZ,Higgs to 4 lepton,Differential measurement,Cross-section measurement,Higgs,ZZ,>=3 leptons

08-APR-2013139 fb-1Documents | 2004.03969 | Inspire
HepData | Internal
HIGGPaperH(125)->4l STXS and couplingsFull Title: Higgs boson production cross-section measurements and their EFT interpretation in the $4\ell$ decay channel at $\sqrt{s}= $13 TeV with the ATLAS detector

Abstract: Higgs boson properties are studied in the four-lepton decay channel (where lepton = $e$, $\mu$) using 139 fb$^{-1}$ of proton$-$proton collision data recorded at $\sqrt{s}$ = 13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio for $H\to ZZ^*$ decay is measured to be $1.34 \pm 0.12$ pb for a Higgs boson with absolute rapidity below 2.5, in good agreement with the Standard Model prediction of $1.33 \pm 0.08$ pb. Cross-sections times branching ratio are measured for the main Higgs boson production modes in several exclusive phase-space regions. The measurements are interpreted in terms of coupling modifiers and of the tensor structure of Higgs boson interactions using an effective field theory approach. Exclusion limits are set on the CP-even and CP-odd `beyond the Standard Model couplings of the Higgs boson to vector bosons, gluons and top quarks.

Keywords: 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,>=3 leptons

07-APR-2013139 fb-1Documents | 2004.03447 | Inspire
HepData | Internal
STDMPaperLund Plane measurement with charged particlesFull Title: Measurement of the Lund jet plane using charged particles in 13 TeV proton-proton collisions with the ATLAS detector

Abstract: The prevalence of hadronic jets at the LHC requires that a deep understanding of jet formation and structure is achieved in order to reach the highest levels of experimental and theoretical precision. There have been many measurements of jet substructure at the LHC and previous colliders, but the targeted observables mix physical effects from various origins. Based on a recent proposal to factorize physical effects, this Letter presents a double-differential cross-section measurement of the Lund jet plane using 139 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton$-$proton collision data collected with the ATLAS detector using jets with transverse momentum above 675 GeV. The measurement uses charged particles to achieve a fine angular resolution and is corrected for acceptance and detector effects. Several parton shower Monte Carlo models are compared with the data. No single model is found to be in agreement with the measured data across the entire plane.

Keywords: 13 TeV,Jets and photons,Differential measurement,Cross-section measurement,All hadronic,2 jets,1 jet,Charged tracks

07-APR-2013140 fb-1Documents | 2004.03540 | Inspire
Rivet | HepData | Briefing | Internal
HIGGConference noteH(125) mass H(125)->4lFull Title: Measurement of the Higgs boson mass in the $H\to ZZ^*\to 4\ell$ decay channel with $pp$ collisions at $\sqrt{s}=13$ TeV corresponding to an integrated luminosity of 139 fb$^{-1}$ with the ATLAS detector at the LHC

Abstract: A measurement of the Higgs boson mass, $m_H$ in the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channel is presented. The data employed were recorded by the ATLAS detector between 2015-2018 in proton-proton collisions delivered by the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s}=13$ TeV and correspond to an integrated luminosity of $139~\text{fb}^{-1}$. An analytic model that takes into account the invariant mass resolution of the four-lepton system on a per-event basis is employed. The measured value of $m_H$ is $124.92\pm0.19\text{(stat.)}^{+0.09}_{-0.06}\text{(syst.)}$~GeV.

Keywords: 13 TeV,H(125) measurements,Higgs to ZZ,Higgs to 4 lepton,Mass measurement,Higgs,ZZ,>=3 leptons

05-APR-2013139 fb-1Documents | Internal
HDBSPaperSearch BSM h(125)->Za, a->jetFull Title: Search for Higgs boson decays into a $Z$ boson and a light hadronically decaying resonance using 13 TeV $pp$ collision data from the ATLAS detector

Abstract: A search for Higgs boson decays into a $Z$ boson and a light resonance in two-lepton plus jet events is performed, using a $pp$ collision dataset with an integrated luminosity of 139 fb$^{-1}$ collected at $\sqrt{s}=13$ TeV by the ATLAS experiment at the CERN LHC. The resonance considered is a light boson with a mass below 4 GeV from a possible extended scalar sector, or a charmonium state. Multivariate discriminants are used for the event selection and for evaluating the mass of the light resonance. No excess of events above the expected background is found. Observed (expected) 95% confidence-level upper limits are set on the Higgs boson production cross section times branching fraction to a $Z$ boson and the signal resonance, with values in the range 17 pb to 340 pb ($16^{+6}_{-5}$ pb to $320^{+130}_{-90}$ pb) for the different light spin-0 boson mass and branching fraction hypotheses, and with values of 110 pb and 100 pb ($100^{+40}_{-30}$ pb and $100^{+40}_{-30}$ pb) for the $\eta_c$ and $J/\psi$ hypotheses, respectively.

Keywords: 13 TeV,NMSSM,Exotic Higgs decays,BSM Higgs searches,BSM search,Higgs,Photon,2 jets,Photons,2 leptons

03-APR-2013139 fb-1Documents | 2004.01678 | Inspire
HepData | Internal
SUSYPaperStop pair, long-lived; displaced vertex and displaced muonFull Title: Search for long-lived, massive particles in events with a displaced vertex and a muon with large impact parameter in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for long-lived particles decaying into hadrons and at least one muon is presented. The analysis selects events that pass a muon or missing-transverse-momentum trigger and contain a displaced muon track and a displaced vertex. The analyzed dataset of proton$-$proton collisions at $\sqrt{s } = 13$ TeV was collected with the ATLAS detector and corresponds to 136 fb$^{-1}$. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particle decays that occur in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are presented as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and interpreted as exclusion limits in scenarios with pair-production of long-lived top squarks that decay via a small $R$-parity-violating coupling into a quark and a muon. Top squarks with masses up to 1.7 TeV are excluded for a lifetime of 0.1 ns, and masses below 1.3 TeV are excluded for lifetimes between 0.01 ns and 30 ns.

Keywords: 13 TeV,Displaced vertex,Stop pair production,Long-lived massive particles,BSM search,Long-lived massive particle,MET,1 lepton

26-MAR-2013136 fb-1Documents | 2003.11956 | Inspire
HepData | Internal
HDBSPaperSearch BSM A/H->tautauFull Title: Search for heavy Higgs bosons decaying into two tau leptons with the ATLAS detector using $pp$ collisions at $\sqrt{s}=13$ TeV

Abstract: A search for heavy neutral Higgs bosons is performed using the LHC Run 2 data, corresponding to an integrated luminosity of 139 fb$^{-1}$ of proton$-$proton collisions at $\sqrt{s}=13$ TeV recorded with the ATLAS detector. The search for heavy resonances is performed over the mass range 0.2$-$2.5 TeV for the $\tau^+\tau^-$ decay with at least one $\tau$-lepton decaying into final states with hadrons. The data are in good agreement with the background prediction of the Standard Model. In the $M_{h}^{125}$ scenario of the Minimal Supersymmetric Standard Model, values of $\tan\beta>8$ and $\tan\beta>21$ are excluded at the 95% confidence level for $m_{A}=1.0$ TeV and $m_{A}=1.5$ TeV, respectively.

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

27-FEB-2013139 fb-1Documents | 2002.12223 | Inspire
HepData | Internal
EXOTPaperDijet resonance in events with at least one leptonFull Title: Search for dijet resonances in events with an isolated charged lepton using $\sqrt{s } = 13$ TeV proton-proton collision data collected by the ATLAS detector

Abstract: A search for dijet resonances in events with at least one isolated charged lepton is performed using $139~{\text{fb}}^{-1}$ of $\sqrt{s}=13$ TeV proton$-$proton collision data recorded by the ATLAS detector at the LHC. The dijet invariant-mass ($m_{jj}$) distribution constructed from events with at least one isolated electron or muon is searched in the region $0.22 < m_{jj} < 6.3$ TeV for excesses above a smoothly falling background from Standard Model processes. Triggering based on the presence of a lepton in the event reduces limitations imposed by minimum transverse momentum thresholds for triggering on jets. This approach allows smaller dijet invariant masses to be probed than in inclusive dijet searches, targeting a variety of new-physics models, for example ones in which a new state is produced in association with a leptonically decaying $W$ or $Z$ boson. No statistically significant deviation from the Standard Model background hypothesis is found. Limits on contributions from generic Gaussian signals with widths ranging from that determined by the detector resolution up to 15% of the resonance mass are obtained for dijet invariant masses ranging from 0.25 TeV to 6 TeV. Limits are set also in the context of several scenarios beyond the Standard Model, such as the Sequential Standard Model, a technicolor model, a charged Higgs boson model and a simplified Dark Matter model.

Keywords: 13 TeV,BSM resonance,BSM search,2 jets,1 lepton

26-FEB-2013139 fb-1Documents | 2002.11325 | Inspire
HepData | Internal
SUSYConference noteStop pair, WIMP DM pair; 1 leptonFull Title: Search for new phenomena with top quark pairs in final states with one lepton, jets, and missing transverse momentum in $\sqrt{s } = 13$ TeV $pp$ collision data with the ATLAS detector.

Abstract: A search for new phenomena with top quark pairs in final states with one isolated electron or muon, multiple jets, and large missing transverse momentum is performed. Signal regions are employed to search for two- and four-body decays of the directly pair-produced supersymmetric partner of the top quark (stop). Additional signal regions are designed specifically to search for spin-0 mediator models, where the mediator is produced in association with a pair of top quarks and decays into a pair of dark matter particles. The search is performed using the Large Hadron Collider proton-proton dataset at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb$^{−1}$. No significant excess from the Standard Model background is observed, and limits at 95% confidence level are set in the stop–neutralino and in the mediator–dark matter particle mass planes. Stops are excluded up to 1200 GeV in the two-body decay scenario. In the four-body scenario stops up to 640 GeV are excluded for a stop–neutralino mass difference of 60 GeV. Scalar and pseudo-scalar dark matter mediators are excluded up to 200 GeV when the coupling strengths of the mediator to standard model and dark matter particles are both equal to one and when the mass of dark-matter is 1 GeV.

Keywords: 13 TeV,Wimp pair with heavy flavour production,Stop pair production,BSM search,Dark matter,Top pair,MET,b-jets,1 lepton

24-FEB-2013139 fb-1Documents | Briefing | Internal
TOPQPaperObservation of tZq single top at 13 TeVFull Title: Observation of the associated production of a top quark and a $Z$ boson in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: Single top-quark production in association with a $Z$ boson is measured in the trilepton channel. The proton-proton collision data collected by the ATLAS experiment from 2015 to 2018 at a centre-of-mass energy of 13 TeV are used, corresponding to an integrated luminosity of 139 $\text{fb}^{-1}$. Events containing three isolated charged leptons (electrons or muons) and two or three jets, one of which is identified as containing a $b$-hadron, are selected. The main backgrounds are from $t\bar{t}Z$ and diboson production. Neural networks are used to improve the background rejection and extract the signal. The measured cross-section for $t\ell^{+}\ell^{-} q$ production, including non-resonant dilepton pairs with $m_{\ell^+\ell^-} > 30$ GeV, is 97 $\pm$ 13 (stat.) $\pm$ 7 (syst.) fb, consistent with the Standard Model prediction.

Keywords: 13 TeV,Single top measurements,MVA / machine learning,Cross-section measurement,>=3 leptons

18-FEB-2013139 fb-1Documents | 2002.07546 | Inspire
Internal
HDBSPaperVBF HH to 4bFull Title: Search for the $HH \rightarrow b \bar{b} b \bar{b}$ process via vector-boson fusion production using proton-proton collisions at $\sqrt{s } = 13$~!TeV with the ATLAS detector

Abstract: A search for Higgs boson pair production via vector-boson fusion (VBF) in the $b\bar{b}b\bar{b}$ final state is carried out with the ATLAS experiment, using 126 fb$^{-1}$ of proton-proton collision data delivered at $\sqrt{s } = 13$ TeV by the Large Hadron Collider. This search is sensitive to VBF production of additional heavy bosons that may decay into Higgs boson pairs, and in a non-resonant topology it can constrain the quartic coupling between the Higgs bosons and vector bosons. No significant excess, relative to the background-only Standard Model expectation, is observed, and limits on the production cross-section are set at the 95% confidence level for a heavy scalar resonance in the context of an extended Higgs sector, and for non-resonant Higgs boson pair production. Interpretation in terms of the coupling between a Higgs boson pair and two vector bosons is also provided: coupling values normalised to the Standard Model expectation of $\kappa_{2V} < -0.56$ and $\kappa_{2V} > 2.89$ are excluded at the 95% confidence level in data.

Keywords: 13 TeV,Di-Higgs production,BSM Higgs searches,BSM resonance,Di-Higgs production,BSM search,VBF,Di-Higgs,b-jets,All hadronic

14-JAN-2013127 fb-1Documents | 2001.05178 | Inspire
HepData | Internal
SUSYPaperChargino-neutralino pair; 3 leptons, weak-scale mass splittingsFull Title: Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in $\sqrt{s}$ = 13 TeV $pp$ collisions with the ATLAS detector

Abstract: A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell $W$ and $Z$ bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of $\sqrt{s}$ = 13 TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$^{-1}$. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015-2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full dataset are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV.

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

18-DEC-1913139 fb-1Documents | 1912.08479 | Inspire
HepData | Internal
SUSYPaperChargino-neutralino pair, slepton pair; soft leptonsFull Title: Searches for electroweak production of supersymmetric particles with compressed mass spectra in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

Abstract: This paper presents results of searches for electroweak production of supersymmetric particles in models with compressed mass spectra. The searches use 139 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider. Events with missing transverse momentum and two same-flavor, oppositely charged, low transverse momentum leptons are selected, and are further categorized by the presence of hadronic activity from initial-state radiation or a topology compatible with vector-boson fusion processes. The data are found to be consistent with predictions from the Standard Model. The results are interpreted using simplified models of $R$-parity-conserving supersymmetry in which the lightest supersymmetric partner is a neutralino with a mass similar to the lightest chargino, the second-to-lightest neutralino or the slepton. Lower limits on the masses of charginos in different simplified models range from 193 GeV to 240 GeV for moderate mass splittings, and extend down to mass splittings of 1.5 GeV to 2.4 GeV at the LEP chargino bounds (92.4 GeV). Similar lower limits on degenerate light-flavor sleptons extend up to masses of 251 GeV and down to mass splittings of 550 MeV. Constraints on vector-boson fusion production of electroweak SUSY states are also presented.

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

28-NOV-1913139 fb-1Documents | 1911.12606 | Inspire
HepData | Briefing | Internal
SUSYPaperStaus; tausFull Title: Search for direct stau production in events with two hadronic $\tau$-leptons in $\sqrt{s } = 13$ TeV $pp$ collisions with the ATLAS detector

Abstract: A search for the direct production of staus in final states with two hadronically decaying tau leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of 139 fb−1, recorded with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of two mass-degenerate staus in simplified models with each stau decaying into the lightest neutralino and one tau lepton. Stau masses from 120 GeV to 390 GeV are excluded at 95 % confidence level for a massless lightest neutralino.

Keywords: 13 TeV,Slepton pair production,BSM search,MET,Taus

15-NOV-1913139 fb-1Documents | 1911.06660 | Inspire
HepData | Briefing | Internal
DAPRPaperRun 2 Data QualityFull Title: ATLAS data quality operations and performance for 2015-2018 data-taking

Abstract: The ATLAS detector at the Large Hadron Collider reads out particle collision data from over 100 million electronic channels at a rate of approximately $100$ kHz, with a recording rate for physics events of approximately 1 kHz. Before being certified for physics analysis at computer centres worldwide, the data must be scrutinised to ensure they are clean from any hardware or software related issues that may compromise their integrity. Prompt identification of these issues permits fast action to investigate, correct and potentially prevent future such problems that could render the data unusable. This is achieved through the monitoring of detector-level quantities and reconstructed collision event characteristics at key stages of the data processing chain. This paper presents the monitoring and assessment procedures in place at ATLAS during 2015-2018 data-taking. Through the continuous improvement of operational procedures, ATLAS achieved a high data quality efficiency, with 95.6% of the recorded proton-proton collision data collected at $\sqrt{s}=13$ TeV certified for physics analysis.

Keywords: 13 TeV,Detector system performance,ATLAS Detector

12-NOV-1913 140 fb-1Documents | 1911.04632 | Inspire
Internal
STDMPaperZ(-->ll) gamma differential cross-sections at 13TeVFull Title: Measurement of the $Z(\rightarrow\ell^+\ell^-)\gamma$ production cross-section in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: The production of a prompt photon in association with a $Z$ boson is studied in proton-proton collisions at a centre-of-mass energy $\sqrt{s } = $ 13 TeV. The analysis uses a data sample with an integrated luminosity of 139 fb$^{-1}$ collected by the ATLAS detector at the LHC from 2015 to 2018. The production cross-section for the process $pp \rightarrow \ell^+\ell^-\gamma+X$ ($\ell = e, \mu$) is measured within a fiducial phase-space region defined by kinematic requirements on the photon and the leptons, and by isolation requirements on the photon. An experimental precision of 2.9% is achieved for the fiducial cross-section. Differential cross-sections are measured as a function of each of six kinematic variables characterising the $\ell^+\ell^-\gamma$ system. The data are compared with theoretical predictions based on next-to-leading-order and next-to-next-to-leading-order perturbative QCD calculations. The impact of next-to-leading-order electroweak corrections is also considered.

Keywords: 13 TeV,Electroweak processes,Differential measurement,Vphoton,Photons,2 leptons

12-NOV-1913139 fb-1Documents | 1911.04813 | Inspire
Rivet | HepData | Internal
EXOTPaperDjiet resonance searchFull Title: Title: Search for new resonances in mass distributions of jet pairs using 139 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for new resonances decaying into a pair of jets is reported using the dataset of proton-proton collisions recorded at $\sqrt{s}=13$ TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to an integrated luminosity of 139 fb$^{-1}$. The distribution of the invariant mass of the two leading jets is examined for local excesses above a data-derived estimate of the Standard Model background. In addition to an inclusive dijet search, events with jets identified as containing $b$-hadrons are examined specifically. No significant excess of events above the smoothly falling background spectra is observed. The results are used to set cross-section upper limits at 95% confidence level on a range of new physics scenarios. Model-independent limits on Gaussian-shaped signals are also reported. The analysis looking at jets containing $b$-hadrons benefits from improvements in the jet flavour identification at high transverse momentum, which increases its sensitivity relative to the previous analysis beyond that expected from the higher integrated luminosity.

Keywords: 13 TeV,Compositeness,BSM resonance,BSM search,b-jets,2 jets

18-OCT-1913139 fb-1Documents | 1910.08447 | Inspire
HepData | Internal
BPHYConference noteJ/psi and psi(2S) differential cross-sections at high pTFull Title: J/psi and psi(2S) differential cross-sections at high pT

Abstract: The measurements of the prompt and non-prompt differential cross-sections of $J/\psi$ and $\psi(2\mathrm{S})$ mesons with $p_{T}$ between 60 and 360 GeV and rapidity range $|y|<2$ are reported. Furthermore, the measurements of the non-prompt fractions of $\psi(2S)$ and $J/\psi$, and prompt and non-prompt production ratios of $\psi(2S)$ to $J/\psi$ are presented. The analysis is performed using $pp$ collision data recorded by the ATLAS detector at $\sqrt{s}=13$ TeC collected between 2015 and 2018, corresponding to $139$~fb$^{-1}$ of integrated luminosity.

Keywords: 13 TeV,Quarkonium,Muon pairs,Non-prompt production,Prompt production,Differential measurement,Cross-section measurement,2 leptons

30-SEP-1913139 fb-1Documents | Internal
HIGGPaperSearch BSM H(125)->emu lepton flavor violating decay and H(125)->eeFull Title: Search for the Higgs boson decays $H \to ee$ and $H \to e\mu$ in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: Searches for the Higgs boson decays $H \to ee$ and $H \to e \mu$ are performed using data corresponding to an integrated luminosity of 139 fb$^{-1}$ collected with the ATLAS detector in $pp$ collisions at $\sqrt{s } = 13$ TeV at the LHC. No significant signals are observed, in agreement with the Standard Model expectation. For a Higgs boson mass of 125 GeV, the observed (expected) upper limit at the 95% confidence level on the branching fraction $\mathcal{B}(H \to ee)$ is $3.6 \times 10^{-4}$ ($3.5 \times 10^{-4} $) and on $\mathcal{B}(H \to e \mu)$ is $6.1\times 10^{-5} $ ($5.8\times 10^{-5}$). These results represent improvements by factors of about five and six on the previous best limits on $\mathcal{B}(H \to ee)$ and $\mathcal{B}(H \to e \mu)$ respectively.

Keywords: 13 TeV,Exotic Higgs decays,LFV,BSM search,2 leptons

23-SEP-1913139 fb-1Documents | 1909.10235 | Inspire
Internal
SUSYPaperChargino-neutralino pair; Higgs boson in final state, 2 b-jets and 1 leptonFull Title: Search for direct production of electroweakinos in final states with one lepton, missing transverse momentum and a Higgs boson decaying into two $b$-jets in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: The results of a search for electroweakino pair production $pp \rightarrow \tilde\chi^\pm_1 \tilde\chi^0_2$ in which the chargino ($\tilde\chi^\pm_1$) decays into a $W$ boson and the lightest neutralino ($\tilde\chi^0_1$), while the heavier neutralino ($\tilde\chi^0_2$) decays into the Standard Model 125 GeV Higgs boson and a second $\tilde\chi^0_1$ are presented. The signal selection requires a pair of $b$-tagged jets consistent with those from a Higgs boson decay, and either an electron or a muon from the $W$ boson decay, together with missing transverse momentum from the corresponding neutrino and the stable neutralinos. The analysis is based on data corresponding to 139 fb$^{-1}$ of $\sqrt{s}=13$ TeV $pp$ collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. No statistically significant evidence of an excess of events above the Standard Model expectation is found. Limits are set on the direct production of the electroweakinos in simplified models, assuming pure wino cross-sections. Masses of $\tilde{\chi}^{\pm}_{1}/\tilde{\chi}^{0}_{2}$ up to 740 GeV are excluded at 95% confidence level for a massless $\tilde{\chi}^{0}_{1}$.

Keywords: 13 TeV,Chargino/neutralino pair production,BSM search,MET,b-jets,1 lepton

19-SEP-1913139 fb-1Documents | 1909.09226 | Inspire
HepData | Internal
SUSYPaperStop pair, sbottom pair, gluino pair; two same-sign leptons or three leptonsFull Title: Search for squarks and gluinos in final states with same-sign leptons and jets using 139 fb$^{-1}$ of data collected with the ATLAS detector

Abstract: A search for supersymmetric partners of gluons and quarks is presented, involving signatures with jets and either two isolated leptons (electrons or muons) with the same electric charge, or at least three isolated leptons. A data sample of proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to a total integrated luminosity of 139 fb$^{-1}$, is used for the search. No significant excess over the Standard Model expectation is observed. The results are interpreted in simplified supersymmetric models featuring both R-parity conservation and R-parity violation, raising the exclusion limits beyond those of previous ATLAS searches to 1600 GeV for gluino masses and 750 GeV for bottom and top squark masses in these scenarios.

Keywords: 13 TeV,RPV SUSY,Stop pair production,Sbottom pair production,Gluino pair production,BSM search,2 leptons (same charge)

18-SEP-1913139 fb-1Documents | 1909.08457 | Inspire
HepData | Internal
TRIGPaperPerformance of the electron and photon triggers of the ATLAS experiment during LHC Run-2Full Title: Performance of electron and photon triggers in ATLAS during LHC Run 2

Abstract: Electron and photon triggers covering transverse energies from 5 GeV to several TeV are essential for the ATLAS experiment to record signals for a wide variety of physics: from Standard Model processes to searches for new phenomena in both proton-proton and heavy-ion collisions. To cope with a fourfold increase of peak LHC luminosity from 2015 to 2018 (Run 2), to 2.1$\times$10$^{34}$cm$^{-2}$s$^{-1}$, and a similar increase in the number of interactions per beam-crossing to about 60, trigger algorithms and selections were optimised to control the rates while retaining a high efficiency for physics analyses. For proton-proton collisions, the single-electron trigger efficiency relative to a single-electron offline selection is at least 75% for an offline electron of 31 GeV, and rises to 96% at 60 GeV; the trigger efficiency of a 25 GeV leg of the primary diphoton trigger relative to a tight offline photon selection is more than 96% for an offline photon of 30 GeV. For heavy-ion collisions, the primary electron and photon trigger efficiencies relative to the corresponding standard offline selections are at least 84% and 95%, respectively, at 5 GeV above the corresponding trigger threshold.

Keywords: 13 TeV,Trigger-level objects,Electron and photon trigger

02-SEP-1913146 fb-1Documents | 1909.00761 | Inspire
Internal
SUSYPaperChargino pair, slepton pair; 2 leptonsFull Title: Search for electroweak production of charginos and sleptons decaying into final states with two leptons and missing transverse momentum in $\sqrt{s}=13$ TeV $pp$ collisions using the ATLAS detector

Abstract: A search for the electroweak production of charginos and sleptons decaying into final states with two electrons or muons is presented. The analysis is based on 139 fb$^{-1}$ of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at $\sqrt{s}=13$ TeV. Three $R$-parity-conserving scenarios where the lightest neutralino is the lightest supersymmetric particle are considered: the production of chargino pairs with decays via either $W$ bosons or sleptons, and the direct production of slepton pairs. The analysis is optimised for the first of these scenarios, but the results are also interpreted in the others. No significant deviations from the Standard Model expectations are observed and limits at 95 % confidence level are set on the masses of relevant supersymmetric particles in each of the scenarios. For a massless lightest neutralino, masses up to 420 GeV are excluded for the production of the lightest-chargino pairs assuming $W$-boson-mediated decays and up to 1 TeV for slepton-mediated decays, whereas for slepton-pair production, masses up to 700 GeV are excluded assuming three generations of mass-degenerate sleptons.

Keywords: 13 TeV,Chargino/neutralino pair production,Slepton pair production,BSM search,MET,1 jet,0 jets,2 leptons

21-AUG-1913139 fb-1Documents | 1908.08215 | Inspire
HepData | Briefing | Internal
HDBSPaperSearch hh->bb WW DileptonFull Title: Search for non-resonant Higgs boson pair production in the $bb\ell\nu\ell\nu$ final state with the ATLAS detector in $pp$ collisions at $\sqrt{s } = 13$ TeV

Abstract: A search for non-resonant Higgs boson pair production, as predicted by the Standard Model, is presented, where one of the Higgs bosons decays via the $H\rightarrow bb$ channel and the other via one of the $H \rightarrow WW^*/ZZ^*/\tau\tau$ channels. The analysis selection requires events to have at least two $b$-tagged jets and exactly two leptons (electrons or muons) with opposite electric charge in the final state. Candidate events consistent with Higgs boson pair production are selected using a multi-class neural network discriminant. The analysis uses 139 fb$^{-1}$ of $pp$ collision data recorded at a centre-of-mass energy of 13 TeV, by the ATLAS detector at the Large Hadron Collider. An observed (expected) upper limit of 1.2 ($0.9^{+0.4}_{-0.3}$) pb is set on the non-resonant Higgs boson pair production cross-section at 95% confidence level, which is equivalent to 40 ($29^{+14}_{-9}$) times the value predicted in the Standard Model.

Keywords: 13 TeV,Di-Higgs production,BSM Higgs searches,Di-Higgs production,Higgs to bb,Higgs to WW,BSM search,Di-Higgs,b-jets,2 leptons

19-AUG-1913139 fb-1Documents | 1908.06765 | Inspire
HepData | Internal
SUSYPaperSbottom; b-jetsFull Title: Search for bottom-squark pair production with the ATLAS detector in final states containing Higgs bosons, $b$-jets and missing transverse momentum

Abstract: The result of a search for the pair production of the lightest supersymmetric partner of the bottom quark ($\tilde{b}_{1}$) using 139 fb$^{-1}$ of proton-proton data collected at $\sqrt{s } = 13$ TeV by the ATLAS detector is reported. In the supersymmetric scenarios considered both of the bottom-squarks decay into a $b$-quark and the second-lightest neutralino, $\tilde{b}_{1} \rightarrow b + \tilde{\chi}^{0}_{2}$. Each $\tilde{\chi}^{0}_{2}$ is assumed to subsequently decay with 100% branching ratio into a Higgs boson ($h$) like the one in the Standard Model and the lightest neutralino: $\tilde{\chi}^{0}_{2} \rightarrow h + \tilde{\chi}^{0}_{1}$. The $\tilde{\chi}^{0}_{1}$ is assumed to be the lightest supersymmetric particle (LSP) and is stable. Two signal mass configurations are targeted: the first has a constant LSP mass of 60 GeV; and the second has a constant mass difference between the $\tilde{\chi}^{0}_{2}$ and $\tilde{\chi}^{0}_{1}$ of 130 GeV. The final states considered contain no charged leptons, three or more $b$-jets, and large missing transverse momentum. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered. Limits at the 95% confidence level are placed in the supersymmetric models considered, and bottom-squarks with mass up to 1.5 TeV are excluded.

Keywords: 13 TeV,Sbottom pair production,BSM search,Higgs,MET,b-jets,0 lepton

08-AUG-1913139 fb-1Documents | 1908.03122 | Inspire
HepData | Briefing | Internal
SUSYConference noteGluino pair; squark pair; gluino-squark; 0-leptonFull Title: Search for squarks and gluinos in final states with jets and missing transverse momentum using 139 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 jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded by the ATLAS experiment in proton--proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$^{-1}$. The results are interpreted in the context of various $R$-parity-conserving models where squarks and gluinos are pair-produced and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.35 TeV for a simplified model considering 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 1.94 TeV are excluded if the lightest neutralino is massless. These limits substantially extend the region of supersymmetric parameter space previously excluded by similar searches with the ATLAS detector.

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

07-AUG-1913139 fb-1Documents | Briefing | Internal
HDBSConference noteDi-muon resonance search in b-jet plus jet plus di-muon eventsFull Title: Search for a new resonance in the $bj\mu\mu$ final state at a dimuon invariant mass around 28 Gev with ATLAS $pp$ data collected at $\sqrt{s } = $ 8 and 13 TeV

Abstract: A search for a resonance decaying to two muons in the dimuon invariant mass range between 26-30 GeV and produced in association with a $b$-jet and an additional jet, is presented. The analysis uses proton-proton collision datasets recorded by the ATLAS detector at the centre-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 20~$\text{fb}^{-1}$ and 139~$\text{fb}^{-1}$, respectively. The events are categorised into two mutually exclusive search regions - the first one with exactly one central jet and at least one forward jet, and the second with at least two central jets and no forward jets. No significant excess above the Standard Model predictions is observed.

Keywords: 8 TeV,BSM resonance,BSM search,b-jets,1 jet,2 leptons,13 TeV

02-AUG-1913139 fb-1Documents | Internal
TOPQConference noteMeasurement of the top-quark decay width in top-quark pair events in the dilepton channel at Sqrt(s) = 13 TeV with the ATLAS detectorFull Title: Measurement of the top-quark decay width in top-quark pair events in the dilepton channel at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A direct measurement of the top-quark decay width using data collected with the ATLAS experiment at $\sqrt{s}=13$ TeV is presented. The data set, collected in the years 2015 to 2018, corresponds to an integrated luminosity of 139 $\mbox{fb\(^{-1}\)}$. The decay width is measured directly using a profile-likelihood template fit to the invariant mass distribution of a charged lepton and the corresponding $b$-jet in the dileptonic decay channel of the top-quark pair. The measured width is $\Gamma_t=1.9 \pm 0.5$ GeV, in agreement with the Standard Model prediction.

Keywords: 13 TeV,Top properties measurements,2 leptons,1 lepton

02-AUG-1913139 fb-1Documents | Internal
HIGGConference noteH(125) combination differential cross-sections gamma gamma and 4lFull Title: Combined measurement of the total and differential cross sections in the $H\to\gamma\gamma$ and $H\to ZZ^*\to 4\ell$ decay channels at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: Combined measurements of the total and differential cross sections of Higgs boson production are performed with proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. The data correspond to an integrated luminosity of 139 $\textrm{fb}^{-1}$ produced at a center-of-mass energy of 13 TeV. The cross sections are obtained from the measured $H \rightarrow ZZ^* \rightarrow 4\ell$ and $H \rightarrow \gamma \gamma$ event yields, which are combined accounting for luminosity, detector effects, acceptances, and branching fractions. The measured total Higgs boson production cross section is 55.4$^{+4.3}_{-4.2}$~pb, in agreement with the Standard Model prediction. A differential cross-section measurement is also performed as a function of the Higgs boson transverse momentum. The results from the two decay channels are found to be compatible with each other, 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

15-JUL-1913139 fb-1Documents | Briefing | Internal
HIGGConference noteH(125)->gammagamma differential cross sectionsFull Title: Measurements and interpretations of Higgs-boson fiducial cross sections in the diphoton decay channel using 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}= $ 13 TeV with the ATLAS detector

Abstract: Fiducial integrated and differential cross sections for the production of the Higgs boson decaying to two photons are measured using 139 fb$^{-1}$ of proton--proton collision data recorded at $\sqrt{s}=13$ TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive production cross section in a fiducial region closely matching the experimental selection of the photons is measured to be 65.2 $\pm$ 7.1 fb, which is in good agreement with the Standard Model prediction of 63.6 $\pm$ 3.3 fb. Differential measurements are performed for a set of variables that are related to the diphoton kinematics as well as the kinematics and multiplicity of the jets produced in association with the Higgs boson. The measurements are compared to various QCD calculations and are found to be in good agreement with the Standard Model predictions. The measurements are also used to probe the strength and tensor structure of the interactions of the Higgs boson using an effective Lagrangian which introduces additional CP-even and CP-odd interactions. In addition, an interpretation of the transverse momentum distribution of the Higgs boson is performed as an indirect probe of the Yukawa coupling of the Higgs boson to the charm quark. Resulting limits on the strength of anomalous interactions are presented for these two approaches.

Keywords: 13 TeV,H(125) measurements,Higgs to 2 photons,Differential measurement,Cross-section measurement,Higgs,Di-photon,Photons

14-JUL-1913139 fb-1Documents | Briefing | Internal
FTAGConference noteSoft b-hadron tagging for compressed SUSY scenariosFull Title: Soft $b$-hadron tagging for compressed SUSY scenarios

Abstract: $b$-hadrons with transverse momenta too low to yield a calorimeter jet that can be efficiently identified by $b$-tagging techniques are ubiquitous in scenarios of compressed spectra of supersymmetric third generation particles. Three different techniques to tag low transverse momentum $b$-hadrons are described and characterised. One of them makes use of jets reconstructed only from tracks, while the other two explore the feasibility and performance of a vertex reconstruction not relying on any jet finding. The approaches are found to be complementary, with the latter two yielding better sensitivity to $b$-hadron transverse momenta in the 5-15 GeV range, and the former providing the best performance above 15 GeV.

Keywords: b-jets,13 TeV,Displaced vertex,b-tag performance,Stop pair production,BSM search,Top pair,b-hadron

10-JUL-1913139 fb-1Documents | Internal
TOPQConference noteMeasurement of ttbar charge asymmetry at 13 TeVFull Title: Inclusive and differential measurement of the charge asymmetry in $t\bar{t}$ events at 13 TeV with the ATLAS detector

Abstract: A measurement of the top-antitop ($t\bar t$) charge asymmetry $A_{\text{C}}$ is presented using data corresponding to an integrated luminosity of 139 fb$^{-1}$ of $\sqrt{s } = 13$ TeV of $pp$ collisions recorded by the ATLAS experiment at the Large Hadron Collider, CERN. The measurement is performed in the single-lepton channel ($e$ or $\mu$) combining both the resolved and boosted topologies of top quark decays. A Bayesian unfolding procedure is used to infer the asymmetry at parton level, correcting for detector resolution and acceptance effects. The inclusive $t\bar t$ charge asymmetry is measured as $A_{\text{C} } = 0.0060 \pm 0.0015 \textrm{(stat+syst.)}$, which differs from zero by 4 standard deviations. Differential measurements are performed as a function of the invariant mass and longitudinal boost of the $t\bar t$ system. Both inclusive and differential measurements are found to be compatible with the Standard Model predictions, at NNLO in perturbation theory with NLO electroweak corrections.

Keywords: 13 TeV,Top properties measurements,ttbar asymmetry measurements,EFT,Differential measurement,Boosted,2 leptons,1 lepton

07-JUL-1913139 fb-1Documents | Briefing | Internal
HDBSPaperDiboson resonance search in the all-hadronic final stateFull Title: Search for diboson resonances in hadronic final states in 139 fb$^{-1}$ of $pp$ 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 139 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 from 2015 to 2018. The diboson system is reconstructed using pairs of high transverse momentum, large-radius jets. These jets are built from a combination of calorimeter- and tracker-inputs compatible with the hadronic decay of a boosted $W$ or $Z$ boson, using jet mass and substructure properties. The search is performed for diboson resonances with masses greater than 1.3 TeV. No significant deviations from the background expectations are observed. Exclusion limits at the 95% confidence level are set on the production cross-section times branching ratio into dibosons for resonances in a range of theories beyond the Standard Model, with the highest excluded mass of a new gauge boson at 3.8 TeV in the context of mass-degenerate resonances that couple predominantly to gauge bosons.

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

20-JUN-1913139 fb-1Documents | 1906.08589 | Inspire
HepData | Internal
EXOTPaperlepton + MET resonance searchFull Title: Search for a heavy charged boson in events with a charged lepton and missing transverse momentum from $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for a heavy charged-boson resonance decaying into a charged lepton (electron or muon) and a neutrino is reported. A data sample of 139 fb$^{-1}$ of proton-proton collisions at $\sqrt{s } = 13$ TeV collected with the ATLAS detector at the LHC during 2015-2018 is used in the search. The observed transverse mass distribution computed from the lepton and missing transverse momenta is consistent with the distribution expected from the Standard Model, and upper limits on the cross section for $pp \to W^\prime \to \ell\nu$ are extracted ($\ell = e$ or $\mu$). These vary between 1.3 pb and 0.05 fb depending on the resonance mass in the range between 0.15 and 7.0 TeV at 95% confidence level for the electron and muon channels combined. Gauge bosons with a mass below 6.0 TeV and 5.1 TeV are excluded in the electron and muon channels, respectively, in a model with a resonance that has couplings to fermions identical to those of the Standard Model $W$ boson. Cross-section limits are also provided for resonances with several fixed $\Gamma / m$ values in the range between 1% and 15%. Model-independent limits are derived in single-bin signal regions defined by a varying minimum transverse mass threshold. The resulting visible cross-section upper limits range between 4.6 (15) pb and 22 (22) ab as the threshold increases from 130 (110) GeV to 5.1 (5.1) TeV in the electron (muon) channel.

Keywords: 13 TeV,BSM resonance,BSM search,MET,1 lepton

13-JUN-1913139 fb-1Documents | 1906.05609 | Inspire
HepData | Internal
DAPRConference noteRun-2 pp luminosityFull Title: Luminosity determination in pp collisions at $\sqrt{s}=13$ TeV using the ATLAS detector at the LHC

Abstract: This note describes the preliminary determination of the integrated luminosity for $pp$ collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS detector during Run 2 of the LHC from 2015-2018. The absolute luminosity scale was determined using van der Meer scans during dedicated running periods in each year, and extrapolated to the physics data-taking regime using complementary measurements from several luminosity-sensitive detectors. The total uncertainties on the integrated luminosities for each individual year of data-taking range from 2.0-2.4 %, and are partially correlated between years. After typical data-quality selections, the full Run 2 $pp$ data sample corresponds to an integrated luminosity of 139 fb$^{−1}$ , with an uncertainty of 1.7%.

Keywords: 13 TeV,Luminosity measurements

29-MAY-1913140 fb-1Documents | Internal
SUSYConference noteStop pair; 1-leptonFull Title: Search for direct top squark pair production in the 3-body decay mode with a final state containing one lepton, jets, and missing transverse momentum in $\sqrt{s}=13$!TeV $pp$ collision data with the ATLAS detector

Abstract: A search for direct pair production of top squarks, the supersymmetric partner of the top quark, is presented. The search focuses on final states with one isolated electron or muon, multiple jets, and large missing transverse momentum. The analysis is performed using the Large Hadron Collider Run 2 proton-proton dataset at a centre-of-mass energy of $\sqrt{s}= $13TeV recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139fb$^{-1}$. One particular signal scenario is considered, characterised by the mass-splitting between the top squark and the lightest neutralino, where each top squark decays via a 3-body process to a $b$ quark, a $W$ boson, and a neutralino. No significant deviation from the predicted Standard Model background is observed, and limits at 95$\%$ confidence level on the supersymmetric benchmark model are set, excluding top squark masses up to 720GeV with neutralino masses up to 580GeV.

Keywords: 13 TeV,Stop pair production,MVA / machine learning,BSM search,Top pair,MET,b-jets,1 lepton

22-MAY-1913139 fb-1Documents | Internal
SUSYConference noteStop pair; Z bosonFull Title: Search for top squarks in events with a Z boson using 139 fb$^{-1}$ of pp collision data at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: A search for direct top squark pair production in events with a same-flavour opposite-sign dilepton pair with invariant mass consistent with a $Z$ boson plus missing transverse momentum is presented. The analysis is performed using the proton-proton collision data at $\sqrt{s}$=13 TeV collected by the ATLAS experiment during the LHC Run-2, corresponding to an integrated luminosity of 139 fb$^{-1}$. No excess is observed in the data with respect to the SM predictions. The results are interpreted in simplified models featuring direct production of pairs of either the lighter top squark ($\tilde{t}_1$) or the heavier top squark ($\tilde{t}_2$), excluding at 95% confidence level $\tilde{t}_1$ and $\tilde{t}_2$ masses up to about 1140 and 875 GeV, respectively.

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

20-MAY-1913139 fb-1Documents | Internal
HIGGConference notetth(125) h->gammagammaFull Title: Measurement of Higgs boson production in association with a tt quark-antiquark pair in the diphoton decay channel using 139 fb$^{-1}$ of LHC data collected at $\sqrt{s}$ = 13 TeV by the ATLAS experiment

Abstract: The measurement of Higgs boson production in association with a top quark-antiquark pair in the diphoton decay channel ($H \to \gamma \gamma$) is presented, based on the analysis of 139~fb$^{-1}$ of proton-proton collision data with center-of-mass energy $\sqrt{s}=13$ TeV recorded with the ATLAS detector at the Large Hadron Collider. The analysis is performed using a simultaneous fit in seven signal-enriched event categories. The $t\bar{t}H$ process is observed in the diphoton decay mode with a significance of 4.9 standard deviations relative to the background-only hypothesis. The expected significance is 4.2 standard deviations. The $t\bar{t}H$ cross-section times the $H \to \gamma \gamma$ branching ratio is measured to be $\sigma_{t\bar{t}H}\times B_{\gamma\gamma } = 1.59_{-0.39}^{+0.43}$~fb, in agreement with the Standard Model prediction.

Keywords: Photons,13 TeV,Coupling measurements,H(125) measurements,ttH production,Higgs to 2 photons,Cross-section measurement,Higgs,Top pair,Di-photon,b-jets

19-MAR-1913139 fb-1Documents | Briefing | Internal
EXOTPaperDilepton Resonance SearchFull Title: Search for high-mass dilepton resonances using 139 fb$^{-1}$ of $pp$ collision data collected at $\sqrt{s}= $13 TeV with the ATLAS detector

Abstract: A search for high-mass dielectron and dimuon resonances in the mass range of 250 GeV to 6 TeV is presented. The data were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}= $13 TeV during Run 2 of the Large Hadron Collider and correspond to an integrated luminosity of 139 fb$^{-1}$. A functional form is fitted to the dilepton invariant-mass distribution to model the contribution from background processes, and a generic signal shape is used to determine the significance of observed deviations from this background estimate. No significant deviation is observed and upper limits are placed at the 95% confidence level on the fiducial cross-section times branching ratio for various resonance width hypotheses. The derived limits are shown to be applicable to spin-0, spin-1 and spin-2 signal hypotheses. For a set of benchmark models, the limits are converted into lower limits on the resonance mass and reach 4.5 TeV for the E6-motivated $Z^\prime_\psi$ boson. Also presented are limits on Heavy Vector Triplet model couplings.

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

14-MAR-1913139 fb-1Documents | 1903.06248 | Inspire
HepData | Briefing | Internal

Object Performance and Trigger results


Topic Document type Short title Reference and Link Release conference
MCP Public plots Muon reconstruction and identification efficiency with 15.8 fb−1 of data collected in 2018 with the ATLAS detector MUON-2018-006 LHCC
Jet/Etmiss CP Public plots Missing transverse energy performance in 2017 and 2018 data JETM-2018-004/ ICHEP
E/gamma CP Public plots Z to ee mass distribution for early 2018 data EGAM-2018-003 LHCP
Muon CP Public plots Muon performance plots with first 2018 data: efficiency, scale and resolution MUON-2018-001/ LHCP

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Topic revision: r8 - 2020-06-02 - GianlucaPicco
 
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