# Summary of ATLAS 13 TeV results using the full 2015 − 2017 data-set

This page provides a compact summary of published and preliminary ATLAS physics and performance results on 13 TeV proton–proton collision data based on the Run-2 data-set taken between 2015 and 2017. 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.

BPHYPaperBs to J/psi phi run-2Full Title: Measurement of the $CP$-violating phase $\phi_s$ in $B^0_s \to J/\psi\phi$ decays in ATLAS at 13 TeV

Abstract: A measurement of the $B^0_s \to J/\psi\phi$ decay parameters using 80.5 fb$^{-1}$ of integrated luminosity collected with the ATLAS detector from 13 TeV proton-proton collisions at the LHC is presented. The measured parameters include the $CP$-violating phase $\phi_s$, the width difference $\Delta\Gamma_{s}$ between the $B^0_s$ meson mass eigenstates and the average decay width $\Gamma_{s}$. The values measured for the physical parameters are combined with those from 19.2 fb$^{-1}$ of 7 TeV and 8 TeV data, leading to the following: \begin{eqnarray*} \phi_s & = & -0.087\phantom{0} \pm 0.036\phantom{0} ~\mathrm{(stat.)} \pm 0.019\phantom{0} ~\mathrm{(syst.)~rad} \\ \Delta\Gamma_{s} & = & \phantom{-}0.0641 \pm 0.0043 ~\mathrm{(stat.)} \pm 0.0024 ~\mathrm{(syst.)~ps}^{-1} \\ \Gamma_{s} & = & \phantom{-}0.6697 \pm 0.0014 ~\mathrm{(stat.)} \pm 0.0015 ~\mathrm{(syst.)~ps}^{-1} \\ \end{eqnarray*} Results for $\phi_s$ and $\Delta\Gamma_{s}$ are also presented as 68% confidence level contours in the $\phi_s$-$\Delta\Gamma_{s}$ plane. Furthermore, the transversity amplitudes and corresponding strong phases are measured. $\phi_s$ and $\Delta\Gamma_{s}$ measurements are in agreement with the Standard Model predictions.

Keywords: 13 TeV,B-physics and light states trigger,Lifetime measurements,Phi_s measurements,CP violation,b-hadron,2 leptons,Charged tracks

20-JAN-201380.5 fb-1Documents | 2001.07115 | Inspire
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EGAMPaperATLAS electron and photon reconstruction and energy calibration with 2015-2017 dataFull Title: Electron and photon performance measurements with the ATLAS detector using the 2015--2017 LHC proton--proton collision data

Abstract: This paper describes the reconstruction of electrons and photons with the ATLAS detector, as employed for measurements and searches exploiting the complete LHC Run 2 dataset. An improved energy clustering algorithm is introduced, and its implications for the measurement and identification of electrons and photons are discussed in detail. Corrections and calibrations that affect performance, including energy calibration, identification and isolation efficiencies, and the measurement of the charge of reconstructed electron candidates are determined using up to 81 fb$^{-1}$ of proton-proton collision data collected at $\sqrt{s}=$ 13 TeV between 2015 and 2017.

Keywords: 13 TeV,Electromagnetic energy calibration,Reconstruction of conversion vertices,Reconstruction of electron tracks,Reconstruction of electromagnetic energy,Photon performance,Photon identification,Photon reconstruction,Electron performance,Electron identification,Electron reconstruction,Photon,Z,Photons,2 leptons,1 lepton

31-JUL-191380 fb-1Documents | 1908.00005 | Inspire
Internal
EXOTPaperHeavy Neutrino search in boosted topologyFull Title: Search for a right-handed gauge boson decayinginto a high-momentum heavy neutrino and acharged lepton in $pp$ collisions with the ATLASdetector at $\sqrt{s}=13$ TeV

Abstract: A search for a right-handed gauge boson $W_{\mathrm{R}}$, decaying into a boosted right-handed heavy neutrino $N_{\mathrm{R}}$, in the framework of Left-Right Symmetric Models is presented. It is based on data from proton-proton collisions with a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015, 2016 and 2017, corresponding to an integrated luminosity of 80 fb$^{-1}$. The search is performed separately for electrons and muons in the final state. A distinguishing feature of the search is the use of large-radius jets containing electrons. Selections based on the signal topology result in smaller background compared with to expected signal. No significant deviation from the Standard Model prediction is observed and lower limits are set in the $W_{\mathrm{R}}$ and $N_{\mathrm{R}}$ mass plane. Mass values of the $W_{\mathrm{R}}$ smaller than 3.8-5 TeV are excluded for $N_{\mathrm{R}}$ in the mass range 0.1-1.8 TeV.

Keywords: 13 TeV,Heavy neutrinos,BSM resonance,BSM search,Boosted,1 jet,2 leptons

29-APR-191380 fb-1Documents | 1904.12679 | Inspire
HepData | Internal
EXOTPaperLow mass dijet resonances with ISR 2017Full Title: Search for low-mass resonances decaying into two jets and produced in association with a photon using $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search is performed for localised excesses in dijet mass distributions of low-dijet-mass events produced in association with a high transverse energy photon. The search uses up to 79.8 fb$^{-1}$ of LHC proton-proton collisions collected by the ATLAS experiment at a centre-of-mass energy of 13 TeV during 2015-2017. Two variants are presented: one which makes no jet flavour requirements and one which requires both jets to be tagged as $b$-jets. The observed mass distributions are consistent with multi-jet processes in the Standard Model. The data are used to set upper limits on the production cross-section for a benchmark $Z^\prime$ model and, separately, on generic Gaussian-shape contributions to the mass distributions, extending the current ATLAS constraints on dijet resonances to the mass range between 225 and 1100 GeV.

Keywords: 13 TeV,BSM resonance,BSM search,ISR,Photon,b-jets,2 jets,Photons

30-JAN-191380 fb-1Documents | 1901.10917 | Inspire
HepData | Internal
EXOTConference noteLow mass boosted di-b-jet resonances with an extra jetFull Title: Search for boosted resonances decaying to two b-quarks and produced in association with a jet at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for new resonances decaying into a pair of bottom quarks in the merged regime is reported using an integrated luminosity of 80.5~\ifb of proton-proton collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. For the resonance to be merged, an extra jet with high transverse momentum is required. The mass range from 70 to 230 GeV is inspected. For the Standard Model Higgs boson, the observed signal strength is $\mu_{H } = 5.8 \pm 3.1~\text{(stat.)}~\pm1.9~\text{(syst.)}~\pm 1.7~\text{(th.)}$, consistent with the background-only hypothesis at $1.6$ standard deviations. No evidence of a significant excess of events beyond the expected background is found and limits on leptophobic $Z^\prime$ bosons with democratic axial couplings to all quark generations are set in the probed mass range.

Keywords: 13 TeV,BSM resonance,BSM search,ISR,Boosted,b-jets,>=3 jets

23-NOV-181380 fb-1Documents | Internal
EXOTConference noteMET + H->bb search 13 TeV 2017Full Title: Search for Dark Matter Produced in Association with a Higgs Boson Decaying to $b\bar{b}$ at $\sqrt{s}=13$ TeV with the ATLAS Detector using 79.8 fb$^{-1}$ of pp collisions

Abstract: A search for dark matter produced in association with a Higgs boson decaying to $b$-quarks is performed using $pp$ collisions at a centre-of-mass energy of $\sqrt{s}= 13\,$TeV. The dataset has an integrated luminosity of 79.8$\,$fb$^{-1}$ and was recorded with the ATLAS detector at the Large Hadron Collider. Selected collision events comprise large missing transverse momentum and either two $b$-tagged small radius jets or a single large radius jet containing two $b$-tagged subjets. The reconstruction of these subjets is based on a jet algorithm that uses inner detector tracks as inputs and a radius parameter that decreases as the subjet transverse momentum increases. The observed data are in agreement with the Standard Model predictions. The results are interpreted in the context of a simplified model ($Z^{\prime}$-2HDM) which describes the interaction of dark matter and Standard Model particles via new heavy mediator particles. Masses of the $Z^{\prime}$ are excluded up to $2.8\,$TeV depending on the choices for other model parameters.

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

24-JUL-181380 fb-1Documents | Internal
EXOTConference noteSingle VLQ search B->bH(gg)Full Title: Search for single vector-like B quarks decaying to a Higgs boson and a bottom quark with the Higgs decaying to a pair of photons

Abstract: A search is presented for single production of a vector-like $B$ quark that decays into a Higgs boson and a $b$ quark. The search uses a dataset corresponding to 79.8 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV collected during 2015-2017 with the ATLAS detector at the Large Hadron Collider. The analysis focuses on the presence of a Higgs boson that decays into two photons, a high-momentum $b$-jet and a forward jet, characteristic of $t$-channel production of the signal process. The main background process is non-resonant diphoton production, with additional small contributions from Standard Model processes containing $H\rightarrow\gamma\gamma$ decays. No significant excess above the background expectation is observed, and upper limits on the signal production cross section are set as a function of the $B$-quark mass. Assuming a generalized coupling $\kappa_B = 0.5$ and doublet branching ratios of 50% for $B\rightarrow Hb$ and $B\rightarrow Zb$, $B$ quarks with masses less than 1210 GeV are excluded at the 95% confidence level.

Keywords: 13 TeV,Vector-like quarks,BSM resonance,BSM search,Higgs,Di-photon,b-hadron,b-jets,Photons

02-JUL-181380 fb-1Documents | Internal
EXOTConference noteSearch for type-III Seesaw heavy leptonsFull Title: Search for type-III seesaw heavy leptons in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for the pair production of heavy leptons ($N^0$, $L^\pm$) 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 79.8 fb$^{-1}$ of integrated luminosity recorded in 2015, 2016 and 2017 by the ATLAS detector at the Large Hadron Collider. The analysis focuses on the $N^0$ and $L^\pm$ decays with intermediate $W$ bosons and yielding two final-state light leptons (electron or muon) of different flavor and charge combinations, with at least two jets and large missing transverse momentum in the final state. The search is optimized in six channels distinguished by the flavor combination and charge product of the final state lepton pair, where same charge or opposite charge final states are considered. Good agreement is observed between the number of events in data and Standard Model predictions. The results are translated into exclusion limits on heavy lepton $m(N^0, L^\pm)$ masses, where $N^0$ and $L^\pm$ are considered mass-degenerate. The observed lower 95 % confidence level limit on the mass of the type-III seesaw heavy leptons, where the branching fractions to all lepton flavors are assumed to be equal, is 560 GeV.

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

30-MAY-181380 fb-1Documents | Internal
EXOTConference noteDijet resonance search in events with leptonsFull Title: Search for resonances in the di-jet mass distribution in events with identified leptons in proton-proton collisions at sqrt(s) = 13 TeV with the ATLAS detector

Abstract: A search for dijet resonances in events with identified leptons is performed using $79.8~{\text{fb}}^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collision data recorded by the ATLAS detector. Dijet invariant mass distributions ranging from $0.22-6.3$ TeV in events with at least one isolated lepton ($e$ or $\mu$) are searched for excesses above background expectations. Selecting events based on the presence of a lepton can probe lower $m_{jj}$ than traditional inclusive dijet searches and targets a large range of new physics models with a final-state lepton. Signatures of such processes include associated production of a $W$ or $Z$ boson. No statistically significant deviation from the background hypothesis is found. In the absence of signals indicating the presence of new physics, limits are calculated based on generic Gaussian signals with a width ranging from that determined by the detector resolution to $15\%$ of the resonance mass. Contributions from a signal with effective cross-section ranging from $50$ fb to $0.1$ fb are excluded in the mass range between 0.25 TeV and 6 TeV.

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

29-MAY-181380 fb-1Documents | Internal
FTAGPaperATLAS b-jet identification performance and efficiency measurement with tt events in pp collisions at 13 TeV Full Title: ATLAS $b$-jet identification performance and efficiency measurement with $t\bar{t}$ events in $pp$ collisions at $\sqrt{s}=13$ TeV

Abstract: The algorithms used by the ATLAS Collaboration during Run 2 of the Large Hadron Collider to identify jets containing $b$-hadrons are presented. The performance of the algorithms is evaluated in the simulation and the efficiency with which these algorithms identify jets containing $b$-hadrons is measured in collision data. The measurement uses a likelihood-based method in a sample of highly enriched in $t\bar{t}$ events. The topology of the $t \to W b$ decays is exploited to simultaneously measure both the jet flavour composition of the sample and the efficiency in a transverse momentum range from 20 GeV to 600 GeV. The efficiency measurement is subsequently compared with that predicted by the simulation. The data used in this measurement, corresponding to a total integrated luminosity of 80.5 fb$^{-1}$, were collected in proton-proton collisions during the years 2015 to 2017 at a centre-of-mass energy $\sqrt{s}=$ 13 TeV. By simultaneously extracting both the efficiency and jet flavour composition, this measurement significantly improves the precision compared to previous results, with uncertainties ranging from 1% to 8% depending on the jet transverse momentum.

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

11-JUL-191380 fb-1Documents | 1907.05120 | Inspire
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HIGGConference notettH(125) to multilepton final states (WW, ZZ, tau tau) Full Title: Analysis of $t\bar{t}H$ and $t\bar{t}W$ production in multilepton final states with the ATLAS detector

Abstract: A search for the associated production of a top-quark pair with the Higgs boson ($t\bar{t}H$) in multilepton final states is presented. The search is based on a dataset of proton--proton collisions at $\sqrt{s}=13~$TeV recorded with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 80 fb$^{-1}$. Six final states, defined by the number and flavour of charged-lepton candidates, and 25 event categories are defined to simultaneously search for the \ttH signal and constrain several leading backgrounds. The $t\bar{t}W$ background normalisation is left unconstrained in the statistical analysis and the resulting $t\bar{t}W$ normalisation is found to be higher than the theoretical prediction. An excess of events consistent with $t\bar{t}H$ production, over the expected background from Standard Model processes, is found with an observed significance of 1.8 standard deviations, compared to an expectation of 3.1 standard deviations. Assuming Standard Model branching fractions, the best-fit value of the $t\bar{t}H$ production cross section is $\sigma_{t\bar{t}H } = 294^{+182}_{-162}$~fb, which is consistent with the Standard Model prediction. The impact on the $t\bar{t}H$ cross section measurement of the assumptions made on the $t\bar{t}W$ background modelling is discussed.

Keywords: 13 TeV,ttH production,Higgs to tautau,Higgs to WW,Higgs to ZZ,ttbar + boson measurements,Cross-section measurement,Higgs,Top pair,MET,b-jets,Taus

16-OCT-191380 fb-1Documents | Internal
HIGGConference noteSelf-coupling constraints from single and double Higgs measurementsFull Title: Constraints on the Higgs boson self-coupling from the combination of single-Higgs and double-Higgs production analyses performed with the ATLAS experiment

Abstract: Constraints on the Higgs boson self-coupling are set by combining the single Higgs boson analyses targeting the $\gamma \gamma$, $ZZ^*$, $WW^*$, $\tau^+ \tau^-$ and $b\bar{b}$ decay channels and the double Higgs boson analyses in the $b\bar{b}b\bar{b}$, $b\bar{b}\tau^+\tau^-$ and $b\bar{b} \gamma \gamma$ decay channels, using data collected at $\sqrt{s } = 13$ TeV with the ATLAS detector at the LHC. The data used in these analyses correspond to an integrated luminosity of up to 79.8 fb$^{-1}$ for single Higgs boson analyses and up to 36.1 fb$^{-1}$ for the double Higgs boson analyses. With the assumption that new physics affects only the Higgs boson self-coupling ($\lambda_{HHH}$), values outside the interval $-2.3<\lambda_{HHH}/\lambda_{HHH}^{\textrm{SM}}< 10.3$ are excluded at 95% confidence level. Results with less stringent assumptions are also provided, introducing additional coupling modifiers for the Higgs boson interactions with the other Standard Model particles.

Keywords: 13 TeV,kappa,Coupling measurements,H(125) measurements,Di-Higgs production,Statistical combination,Di-Higgs,Higgs

11-OCT-191380 fb-1Documents | Internal
HIGGPaperH(125) combination cross-sections, couplingsFull Title: Combined measurements of Higgs boson production and decay using up to $80$ fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=$ 13 TeV collected with the ATLAS experiment

Abstract: Combined measurements of Higgs boson production cross sections and branching fractions are presented. The combination is based on the analyses of the Higgs boson decay modes $H \rightarrow \gamma\gamma$, $ZZ^\ast$, $WW^\ast$, $\tau\tau$, $b\bar{b}$, $\mu\mu$, searches for decays into invisible final states, and on measurements of off-shell Higgs boson production. Up to $79.8$ fb$^{-1}$ of proton-proton collision data collected at $\sqrt{s}=$ 13 TeV with the ATLAS detector are used. Results 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 is determined to be $\mu = 1.11^{+0.09}_{-0.08}$. The combined measurement yields an observed (expected) significance for the vector-boson fusion production process of $6.5\sigma$ ($5.3\sigma$). 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 and in the simplified Minimal Supersymmetric Standard Model. No significant deviations from Standard Model predictions are observed.

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

06-SEP-191380 fb-1Documents | 1909.02845 | Inspire
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HIGGPaperVh(125) h->bb STXSFull Title: Measurement of $VH$, $H\to b\bar{b}$ production as a function of the vector-boson transverse momentum in 13 TeV $pp$ collisions with the ATLAS detector

Abstract: Cross-sections of associated production of a Higgs boson decaying into bottom-quark pairs and an electroweak gauge boson, $W$ or $Z$, decaying into leptons are measured as a function of the gauge boson transverse momentum. The measurements are performed in kinematic fiducial volumes defined in the `simplified template cross-section framework. The results are obtained using 79.8 fb$^{-1}$ of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. All measurements are found to be in agreement with the Standard Model predictions, and limits are set on the parameters of an effective Lagrangian sensitive to modifications of the Higgs boson couplings to the electroweak gauge bosons.

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

11-MAR-191380 fb-1Documents | 1903.04618 | Inspire
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HIGGPaperObservation of H->bb and VH productionFull Title: Observation of $H \rightarrow b\bar{b}$ decays and $VH$ production with the ATLAS detector

Abstract: A search for the decay of the Standard Model Higgs boson into a $b\bar{b}$ pair when produced in association with a $W$ or $Z$ boson is performed with the ATLAS detector. The data, corresponding to an integrated luminosity of 79.8 $\mathrm{fb}^{-1}$ were collected in proton-proton collisions during Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.9 (4.3) standard deviations. A combination with the results from other searches in Run 1 and in Run 2 for the Higgs boson in the $b\bar{b}$ decay mode is performed, which yields an observed (expected) significance of 5.4 (5.5) standard deviations, thus providing direct observation of the Higgs boson decay into $b$-quarks. The ratio of the measured event yield for a Higgs boson decaying into $b\bar{b}$ to the Standard Model expectation is $1.01 \pm 0.12 \mathrm{(stat.)} ^{+0.16}_{-0.15} \mathrm{(syst.)}$. Additionally, a combination of Run 2 results searching for the Higgs boson produced in association with a vector boson yields an observed (expected) significance of 5.3 (4.8) standard deviations.

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

24-AUG-181380 fb-1Documents | 1808.08238 | Inspire
Briefing | Internal
HIGGConference noteh(125) -> gamma gamma fiducial differential cross-sections, STXS, couplingsFull Title: Measurement of Higgs boson properties in the diphoton decay channel using 80~fb$^{-1}$ of pp collision data at $\sqrt{s}=$13 TeV with the ATLAS detector

Abstract: This note reports measurements of Higgs boson properties in the two-photon final state using 79.8 fb$^{-1}$ of data recorded at $\sqrt{s}=13$ TeV by the ATLAS experiment at the Large Hadron Collider. The cross sections of Higgs boson production through gluon--gluon fusion, vector-boson fusion, and in association with a vector boson or a top-quark pair are measured. Measurements of the Higgs boson production divided further into kinematic regions, called simplified template cross sections, are also reported. Additionally, the cross section for the production of the Higgs boson decaying to two isolated photons is measured in a fiducial phase space designed to closely match the ATLAS detector acceptance, and is found to be 60.4 $\pm$ 6.1 (stat.) $\pm$ 6.0 (exp.) $\pm$ 0.3 (theo.) fb, in agreement with the Standard Model prediction of 63.5 $\pm$ 3.3 fb. Finally, the fiducial cross section is measured differentially in bins of several kinematic observables with sensitivity to properties of the Higgs boson. Among these, the number of $b$-jets produced in association with the Higgs boson is measured to probe Higgs production in association with heavy flavor hadrons. No significant deviations between the observed data and the Standard Model prediction are observed.

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

04-JUL-181380 fb-1Documents | Internal
HIGGConference noteSearch BSM H-> gamma gammaFull Title: Search for Scalar Diphoton Resonances

Abstract: A search for low-mass diphoton resonances is performed using 80 fb$^{-1}$ of $pp$ collision data collected with the ATLAS detector at the Large Hadron Collider. Pairs of isolated photon candidates with high transverse momentum are selected, probing the diphoton invariant mass spectrum in the range 65 to 110 GeV. No significant excess with respect to the Standard Model expectation is found, and a limit at the 95% confidence level is set on narrow resonance fiducial cross-section times branching ratio ranging from 30 to 101 fb.

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

03-JUL-181380 fb-1Documents | Internal
HIGGPaperObservation of ttH productionFull Title: Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector

Abstract: The observation of Higgs boson production in association with a top quark pair ($t\bar{t}H$), based on the analysis of proton--proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider, is presented. Using data corresponding to integrated luminosities of up to 79.8 fb$^{-1}$, and considering Higgs boson decays into $b\bar{b}$, $WW^*$, $\tau\tau$, $\gamma\gamma$, and $ZZ^*$, the observed significance is 5.8 standard deviations, compared to an expectation of 4.9 standard deviations. Combined with the $t\bar{t}H$ searches using a dataset corresponding to integrated luminosities of 4.5 fb$^{-1}$ at 7 TeV and 20.3 fb$^{-1}$ at 8 TeV, the observed (expected) significance is 6.3 (5.1) standard deviations. Assuming Standard Model branching fractions, the total $t\bar{t}H$ production cross section at 13 TeV is measured to be 670 $\pm$ 90 (stat.) $^{+110}_{-100}$ (syst.) fb, in agreement with the Standard Model prediction.

Keywords: 13 TeV,Coupling measurements,H(125) measurements,ttH production,Higgs to 4 lepton,Higgs to 2 photons,Statistical combination,Cross-section measurement,Higgs,ZZ,Photon,Photons,>=3 leptons

01-JUN-181380 fb-1Documents | 1806.00425 | Inspire
Briefing | Internal
JETMConference noteJet mass response measurement using Forward Folding   Full Title: Measurement of the ATLAS Detector Jet Mass Response using Forward Folding with 80 fb-1 of sqrt(s) = 13 TeV pp data

Abstract: This note reports a measurement of the jet mass response of large-radius jets reconstructed by the ATLAS experiment using $80~\mbox{fb$^{-1}$}~$of $\sqrt{s}=13~\text{TeV}~pp$ data. The response is defined as the distribution of the measured mass given the particle-level jet mass and is characterised by its central value (jet mass scale) and spread (jet mass resolution). In order to account for non-Gaussian behavior of the response as well as non-trivial contributions from the intrinsic particle-level jet mass probability density, the forward-folding method is chosen for the measurement. This procedure is applied to both a top-quark pair final state (200 GeV<$p_\text{T}$<600 GeV for $W$ boson jets and 350 GeV <$p_\text{T}$<1000 GeV for top-quark jets) as well as inclusive $W/Z$+jets events (500 GeV<$p_\text{T}$<1200 GeV). Results are presented for trimmed anti-$k_t$ $R=1.0$ jets built using only calorimeter information as well as for the track-assisted jet mass that combines calorimeter and tracker information, and for reclustered small-radius jets also using $R=1.0$. This note extends previous results by including more data, incorporating the $W/Z$+jets final state, and by comparing various jet mass definitions. In addition, the jet mass response is studied for different numbers of subjets within reclustered jets and found to be universal. For both the jet mass scale and jet mass resolution, good agreement is observed between the data and simulated samples. Uncertainties are evaluated to be 1--5\% for the scale and 10--20\% for the resolution and they are driven by the parton shower and hadronisation modelling.

<p style="font-size:0.8em;color:grey;">Keywords: 13 TeV,Jet mass scale,Top pair,Z,W,Boosted

18-JUL-201380 fb-1Documents | Internal
JETMPaperJet energy scale and resolution calibration in Run 2Full Title: Jet energy scale and resolution measured in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: Jet energy scale and resolution measurements with their associated uncertainties are reported for jets using 36-81 fb$^{-1}$ of proton-proton collision data with a centre-of-mass energy of $\sqrt{s}=13$ TeV collected by the ATLAS detector at the LHC. Jets are reconstructed using two different input types: topo-clusters formed from energy deposits in calorimeter cells, as well as an algorithmic combination of charged-particle tracks with those topo-clusters, referred to as the ATLAS particle-flow reconstruction method. The anti-$k_t$ jet algorithm with radius parameter $R=0.4$ is the primary jet definition used for both jet types. Jets are initially calibrated using a sequence of simulation-based corrections. Next, several \textit{in situ} techniques are employed to correct for differences between data and simulation and to measure the resolution of jets. The systematic uncertainties in the jet energy scale for central jets ($|\eta|<1.2$) vary from 1\% for a wide range of high-$p_{\text{T}}$ jets ($250<p_{\text{T}}<2000$ GeV), to 5\% at very low $p_{\text{T}}$ (20 GeV) and 3.5\% at very high $p_{\text{T}}$ ($>2.5$ TeV). The relative jet energy resolution is measured and ranges from ($24 \pm 1.5$)\% at 20 GeV to ($6 \pm 0.5$)\% at 300 GeV.

Keywords: 13 TeV,Jet energy calibration,All hadronic

06-JUL-201380 fb-1Documents | 2007.02645 | Inspire
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STDMPaperTriboson WVV Analysis at 13 TeVFull Title: Evidence for the production of three massive vector bosons with the ATLAS detector

Abstract: A search for the production of three massive vector bosons in proton-proton collisions is performed using data at $\sqrt{s } = 13$ TeV recorded with the ATLAS detector at the Large Hadron Collider in the years 2015-2017, corresponding to an integrated luminosity of $79.8$ fb$^{-1}$. Events with two same-sign leptons $\ell$ (electrons or muons) and at least two reconstructed jets are selected to search for $WWW \to \ell \nu \ell \nu qq$. Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for $WWW \to \ell \nu \ell\nu \ell \nu$, while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for $WWZ \to \ell \nu qq \ell \ell$. Finally, events with four leptons are analysed to search for $WWZ \to \ell \nu \ell \nu \ell \ell$ and $WZZ \to qq \ell \ell \ell \ell$. Evidence for the joint production of three massive vector bosons is observed with a significance of 4.1 standard deviations, where the expectation is 3.1 standard deviations.

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

25-MAR-191380 fb-1Documents | 1903.10415
HepData | Internal
SUSYConference noteChargino pair; 2 leptonFull Title: Search for direct chargino pair production with W -boson mediated decays in events with two leptons and missing transverse momentum in the final state at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: The results of a search for the direct pair production of charginos decaying via W-bosons are reported using 80.5 fb-1 of integrated luminosity from LHC $pp$ collisions at 13 TeV collected by the ATLAS detector in the 2015, 2016 and 2017 data taking campaigns. Charginos are searched for in final states with two isolated leptons (electron or muon), missing transverse momentum and at most one light jet in the final state. No excess above Standard Model expectations is observed. Exclusion limits are derived on the chargino mass assuming a simplified model in which it decays with a 100% branching ratio to an on-shell W-boson and the lightest neutralino: $\tilde{\chi}_1^\pm \rightarrow W^\pm \tilde{\chi}_1^{0}$. For a massless neutralino, chargino masses up to 410~GeV are excluded at 95% confidence level.

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

25-JUL-181380 fb-1Documents | Internal
SUSYConference noteGluino pair; 0-1 leptons, many b-jetsFull Title: Search for supersymmetry in final states with missing transverse momentum and multiple b-jets in proton-proton collisions at $\sqrt{s}$=13 TeV with the ATLAS detector

Abstract: A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino ($\displaystyle\tilde\chi^0_1$) is reported. It uses LHC proton-proton collision data at a centre-of-mass energy $\sqrt{s } = 13$ TeV with an integrated luminosity of 79.9 fb$^{-1}$ collected with the ATLAS detector from 2015 to 2017. The search is performed in events containing large missing transverse momentum and several energetic jets, at least three of which must be identified as originating from $b$-quarks. No excess is found above the predicted background. For $\displaystyle\tilde\chi^0_1$ masses below approximately 800 GeV, gluino masses of less than 2.23 TeV (2.19) TeV are excluded at 95 % confidence level in simplified models involving the pair production of gluinos that decay via top (bottom) squarks. An interpretation of the limits in terms of the branching ratios of the gluinos into third-generation squarks is also provided.

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

24-JUL-181380 fb-1Documents | Internal
SUSYConference noteSbottom; b-jetsFull Title: Search for bottom-squark pair production with the ATLAS detector in final states containing Higgs bosons, b-jets and ETMiss in pp collisions at $\sqrt{s}$=13 TeV

Abstract: The result of a search for the production of the supersymmetric partner of the bottom-quark ($\tilde{b}_{1}$) using $79.8\,\mathrm{fb}^{-1}$ of data collected at $\sqrt{s } = 13\,\mathrm{TeV}$ by the ATLAS detector in Run 2 is reported. In the supersymmetric scenarios considered the bottom-squarks decay to a $b$-quark and the second lightest neutralino, $\tilde{b}_{1} \rightarrow b + \tilde{\chi}^{0}_{2}$. The $\tilde{\chi}^{0}_{2}$ is assumed to subsequently decay with $100\%$ branching ratio to the Standard-Model-like Higgs boson ($h$) 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 $60\,\mathrm{GeV}$; and the second has a constant mass difference between the $\tilde{\chi}^{0}_{2}$ and $\tilde{\chi}^{0}_{1}$ of $130\,\mathrm{GeV}$. The final states considered contain zero 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 simplified models considered, and bottom-squarks with mass up to $1400\,\mathrm{GeV}$ are excluded.

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

23-JUL-181380 fb-1Documents | Internal
SUSYConference noteZh, h>neutralinos; photonsFull Title: Search for Standard Model Higgs boson decays to at least one photon and missing transverse momentum using 80 fb$^{-1}$ of proton--proton collisions collected at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: A search for Standard Model Higgs bosons decaying into at least one photon and missing transverse momentum is performed using 79.8 fb$^{-1}$ of protonâ€“proton collisions collected at $\sqrt{s}=13$ TeV with the ATLAS detector, where the photon can arise from a neutralino decaying into a gravitino. Higgs bosons produced in association with a $Z$ boson are considered in order to reduce the number of background events. No excess with respect to the Standard Model prediction is observed. Assuming a Standard Model $Zh$ production cross-section, the branching fraction of a Higgs boson to neutralinos or neutralino/gravitino is constrained to be less than 5â€“11% at the 95% confidence level for near massless gravitinos.

Keywords: 13 TeV,GGM/GMSB,VH production,BSM search,Photon,Z,MET,Photons,2 leptons

30-MAY-181380 fb-1Documents | Internal
TOPQPaperSearch for FCNC tqgamma in single topFull Title: Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb$^{-1}$ of $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS experiment

Abstract: A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb$^{-1}$ of proton-proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a $b$-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the $tq\gamma$ coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC $t\gamma$ production via a left-handed (right-handed) $tu\gamma$ coupling of 36 fb (78 fb) and on the branching ratio for $t\rightarrow \gamma u$ of $2.8\times 10^{-5}$ ($6.1\times 10^{-5}$). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC $t\gamma$ production via a left-handed (right-handed) $tc\gamma$ coupling of 40 fb (33 fb) and on the branching ratio for $t\rightarrow \gamma c$ of $22\times 10^{-5}$ ($18\times 10^{-5}$).

Keywords: 1 lepton,Single top rare production,EFT,BSM search,Photons

22-AUG-191380 fb-1Documents | 1908.08461 | Inspire
HepData | Internal
TOPQConference noteSearch for charged lepton flavour violation in top quark decaysFull Title: Search for charged lepton flavour violation in top quark decays at the LHC with the ATLAS detector

Abstract: A direct search for charged lepton-flavour violation in top-quark decays is presented. The data analysed correspond to 79.8 $\text{fb}^{-1}$ of proton-proton collisions at a centre-of-mass energy of $\sqrt{s}= 13$ TeV delivered by the LHC. The process studied is the production of top-quark pairs, where one top quark decays into a pair of opposite-sign different-flavour charged leptons and an up-type quark, while the other decays semileptonically according to the Standard Model. The signature of the signal is thus characterised by the presence of three charged leptons, a light jet and a $b$-jet. A multivariate discriminant is deployed and its distribution used as input to extract the signal strength. In the absence of a signal, an upper limit on the branching ratio of ${\cal B}(t \to \ell \ell q) < 1.86 \times 10^{-5}$ is set at 95% confidence level.

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

12-SEP-181380 fb-1Documents | Internal

## Object Performance and Trigger

Topic Document type Short title Reference and Link Release conference
E/gamma Public plots Photon identification and isolation efficiency measurements in 2017 data : evolution versus ET and pileup EGAM-2018-007 ICHEP
E/gamma Public plots Electron isolation efficiency measurements in 2017 data : evolution versus pT,η and pileup EGAM-2018-006/ ICHEP
E/gamma Public plots Electron identification discriminating variables and efficiency measurements in 2017 data : evolution versus pileup EGAM-2018-005 ICHEP
E/gamma Public plots EGAM-2018-004: Z to ee mass distribution for 2017 data : comparison of low-mu and standard runs EGAM-2018-004 ICHEP
Tau CP Public plots Tau Identification and Energy Scale performance TAU-2018-001 LHCP
Muon CP Public plots Optimization of Isolation Selection at High-mu MUON-2018-002 LHCP
Flavour tag CP Public plots Flavour tagging performance with full 2017 data-set FTAG-2017-008/ LHCC
Egamma CP Public plots Electron efficiency measurements in 2017 data and electron identification discriminating variables from 2016 data EGAM-2018-002 LHCC
Jet/Etmiss CP Public plots Missing transverse energy performance in 2017 data and Monte Carlo using EMTopo Jets JETM-2018-001 LHCC
Tracking CP Public plots Vertexing performance IDTR-2017-008 LHCC
Tracking CP Public plots Average number of tracks IDTR-2017-007 LHCC
E/gamma CP Public plots Performance of electron and photon reconstruction and identification with 2017 data EGAM-2017-010 LHCC
Jet/Etmiss CP Public plots Missing transverse energy performance in 2017 data JETM-2017-011 LHCC
Muon CP Public plots High-µ Muon Reconstruction and Isolation Studies on 2017 Data MUON-2017-005 LHCC
Flavour tag CP Public plots Flavour tagging performance FTAG-2017-008 LHCC
Jet/Etmiss CP Public plots Jet multiplicity vs number of pile-up interactions JETM-2017-009
Jet/Etmiss CP Public plots Relative jet response obtained with eta-intercalibration for 2017 data JETM-2017-008/
E/gamma CP Public plots Z to ee mass as a function of pile-up in 2017 data EGAM-2017-009
Flavour tag CP Public plots Flavour tagging data/simulation plots with 2017 data FTAG-2017-006

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Topic revision: r14 - 2018-09-15 - TancrediCarli

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