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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 proton–proton 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
DAPRConference noteRun2 pp luminosity   Full 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

03-JUN-1913140 fb-1Documents | Internal
EXOTPaperlepton + MET resonance search   Full 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
Internal
EXOTConference noteDijet resonance searchFull Title: Search for New Phenomena in Dijet Events using 139 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV collected with the ATLAS Detector

Abstract: A search for new resonances decaying into two hadronic jets is reported using the entire 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 dijet invariant mass distribution is compared to a smoothly-falling background prediction obtained by fitting the data. No significant excess is observed. Excited quarks with masses below 6.7 TeV are excluded at the 95% confidence level. Model-independent limits on Gaussian-shaped signals of various widths in dijet mass distribution are also set.

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

17-MAR-1913139 fb-1Documents | 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
HDBSConference noteDiboson resonance search in the all-hadronic final state   Full Title: Diboson resonance search in the all-hadronic final state

Abstract: Narrow resonances decaying into $WW$, $WZ$ or $ZZ$ boson pairs are searched for in 139 fb$^{-1}$ of proton-proton 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 a range of theories beyond the Standard Model, with the highest excluded mass of a new gauge boson at 3.6 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-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: 13 TeV,Coupling measurements,H(125) measurements,ttH production,Higgs to 2 photons,Cross-section measurement,Higgs,Top pair,Di-photon,b-jets,Photons

18-MAR-1913139 fb-1Documents | Briefing | Internal
SUSYConference noteStop pair, sbottom pair, gluino pair; two same-sign leptons or three leptons   Full 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, extending the exclusion limits from previous searches up 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)

17-MAY-1913139 fb-1Documents | Internal
SUSYConference noteChargino-neutralino pair; Higgs boson in final state, 2 photons   Full Title: Search for direct production of electroweakinos in final states with missing transverse energy 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. This study is based on the full Run 2 data collected between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of $139~\mathrm{fb}^{-1}$ 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 physics processes. In the context of simplified supersymmetric models, 95% confidence-level limits of up to 315 GeV in $m(\tilde{\chi}^{\pm}_{1}/\tilde{\chi}^{0}_{2})$, where $m(\tilde{\chi}^{0}_{1})$ is 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 $m(\tilde{\chi}^{0}_{1})$.

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

17-MAY-1913139 fb-1Documents | Internal
SUSYConference noteChargino-neutralino pair; 3 leptons, weak-scale mass splittings   Full 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 splitting near the electroweak scale decaying via on-shell $W$ and $Z$ bosons is presented in a three-lepton final state. The analyzed proton-proton collision data taken at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV was 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 with the 2015-2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are consistently 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 between 100 GeV and 350 GeV.

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

19-MAY-1913139 fb-1Documents | Internal
SUSYConference noteStop pair; 1-lepton   Full 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

19-MAY-1913139 fb-1Documents | Internal
SUSYConference noteChargino-neutralino pair, slepton pair; soft leptons   Full 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 note 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, two same-flavour, oppositely-charged, low transverse momentum leptons, and hadronic activity from initial state radiation are selected. 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 a chargino, heavier neutralino, or slepton. Lower limits on the masses of charginos in different simplified models range from 162 GeV to 205 GeV for moderate mass splittings, and extend down to mass splittings of 2 GeV to 2.6 GeV at the LEP chargino bounds. Similar lower limits on degenerate light-flavour sleptons reach up to masses of 256 GeV and down to mass splittings of 590 MeV.

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

19-MAY-1913139 fb-1Documents | Briefing | Internal
SUSYConference noteStop pair; Z boson   Full 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

17-MAY-1913139 fb-1Documents | Internal
SUSYConference noteStaus; taus   Full Title: Search for direct stau production in events with two hadronic tau leptons in $\sqrt{s}$ = 13 TeV p p 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

17-MAY-1913139 fb-1Documents | Briefing | Internal
SUSYConference noteSbottom pair; 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 in pp collisions at $\sqrt{s}=13$ TeV

Abstract: The result of a search for the pair production of the supersymmetric partner of the bottom-quark ($\tilde{b}$) using 139 fb$^{-1}$ of data collected at $\sqrt{s } = 13$ TeV by the ATLAS detector in Run 2 is reported. In the supersymmetric scenarios considered, each of the bottom-squarks decay to a $b$-quark and the second lightest neutralino, $\tilde{b} \rightarrow b + \tilde{\chi}_{2}^{0}$. Each $\tilde{\chi}_{2}^{0}$ is assumed to subsequently decay with 100% branching ratio to the Standard-Model-like Higgs boson ($h$) and the lightest neutralino: $\tilde{\chi}_{2}^{0} \rightarrow h + \tilde{\chi}_{1}^{0}$. The $\tilde{\chi}_{1}^{0}$ 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 $\tilde{\chi}_{2}^{0}$ and $\tilde{\chi}_{1}^{0}$ 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 1.45 TeV are excluded.

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

26-MAR-1913139 fb-1Documents | Briefing | Internal
SUSYConference noteChargino pair, slepton pair; 2 leptonsFull Title: Search for electroweak production of charginos and sleptons decaying in final states with two leptons and missing transverse momentum in $\sqrt{s}=13$ $pp$ 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 to target the first of these scenarios, but its results are also interpreted in the other ones. No significant deviations from the Standard Model expectations are observed and stringent limits at 95\% confidence level are set on the masses of relevant supersymmetric particles in each of these 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

18-MAR-1913139 fb-1Documents | Briefing | Internal
SUSYConference noteStop pair, long-lived; displaced vertex and displaced muonFull Title: Search for long-lived, massive particles in events with a displaced vertex and muon in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: A search for long-lived particles decaying into at least one muon and hadrons is presented. The analysis selects events that pass a muon or missing-transverse-momentum trigger and contain a displaced muon and a displaced vertex with at least three tracks and a visible invariant vertex mass of at least 20~GeV. 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. Background estimates for Standard Model processes and instrumental effects are extracted entirely 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 on scenarios with pair-production of long-lived top squarks that decay via a small $R$-parity-violating coupling to 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 all lifetimes between 0.01~ns and 30~ns.

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

18-MAR-1913136 fb-1Documents | 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: r6 - 2019-02-27 - AndreasHoecker
 
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