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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
SUSYPaperSbottom; b-jets   Full 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
Internal
HIGGConference noteSearch BSM H(125)->emu lepton flavor violating decay and H(125)->ee   Full Title: Search for the decays of the Higgs boson $H\to ee$ and $H\to e\mu$ in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract: Searches for the decay of the Higgs boson $H \to ee$ and $H \to e \mu$ are performed using data corresponding to an integrated luminosity of 139 bf$^{-1}$ 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 of $H \to ee$ is $3.6 \times 10^{-4}$ ($3.5 \times 10^{-4}$) and on $H \to e\mu$ is $6.1\times 10^{-5}$ ($5.8\times 10^{-5}$). These results represent an improvement of a factor of about 5 and 6 on the previous best limits on the branching fractions of $H \to ee$ and $H \to e \mu$, respectively.

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

05-AUG-1913139 fb-1Documents | Briefing | Internal
SUSYConference noteGluino pair; squark pair; gluing-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 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

05-AUG-1913139 fb-1Documents | Internal
TOPQConference noteTop width measurement in dilepton ttbar   Full 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
HDBSConference notedimuon search +bj 8 TeV +13 TeV   Full 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

31-JUL-1913139 fb-1Documents | Internal
STDMConference noteLund Plane measurement with charged particles   Full Title: Measurement of the Lund Jet Plane using charged particles with the ATLAS detector from 13 TeV proton--proton collisions

Abstract: The prevalence of hadronic jets at the Large Hadron Collider (LHC) requires that a deep understanding of jet formation and structure must be 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 new proposal to factorize physical effects, this note presents a double-differential cross section measurement of the Lund jet plane using 139 fb$^{-1}$ of $\sqrt{s}= $13 TeV $pp$ data collected with the ATLAS detector. 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. Multiple parton shower Monte Carlo simulations are compared with data to study the modeling of various physical effects across the plane.

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

24-JUL-1913140 fb-1Documents | Internal
STDMConference noteObservation of electroweak production of two jets in association with a Z-boson pairFull Title: Observation of electroweak production of two jets in association with a $Z$-boson pair in $pp$ collisions at $\sqrt{s } = 13$ TeV with the ATLAS detector

Abstract: This note reports on the observation of electroweak production of two jets in association with a $Z$-boson pair using 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s } = $ 13 TeV collected by the ATLAS detector at the LHC. Two different final states originating from the decays of the $Z$ boson pair, one containing four charged leptons, and the other two charged leptons and two neutrinos, are considered. A significant deviation from the background-only hypothesis is observed, which corresponds to a statistical significance of 5.5 $\sigma$. The observed excess is compatible with the electroweak production of two jets in association with a $Z$-boson pair. In addition, cross-sections for inclusive production of $ZZ$ plus two jets, as well as the observed signal strength of the EW production, are reported.

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

12-JUL-1913139 fb-1Documents | Internal
STDMConference noteZ(-->ll) gamma cross section at 13TeVFull Title: Measurement of $Z\gamma\to\ell^+\ell^-\gamma$ differential cross-sections 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 between 2015 and 2018. Measurements are made of differential cross-sections for the process $pp\to\ell^+\ell^-\gamma+X$ ($\ell = e, \mu$), within a fiducial phase space region dominated by events with a photon produced in addition to a $Z$ decaying to leptons. Cross-sections are shown as a function of each of four kinematic variables characterising the $\ell^+\ell^-\gamma$ system. The data are compared to theoretical predictions based on next-to-leading-order and next-to-next-to-leading-order perturbative QCD calculations.

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

12-JUL-1913139 fb-1Documents | 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: 13 TeV,b-tag performance,Stop pair production,Displaced vertex,BSM search,Top pair,b-hadron,b-jets

11-JUL-1913139 fb-1Documents | Internal
HDBSConference noteVBF HH to 4bFull Title: Search for $HH \rightarrow b\overline{b}bb\overline{b}$ production via vector boson fusion 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 detector, 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 to Higgs boson pairs, and in a non-resonant topology it can constrain the parameters of pairs of Higgs bosons coupling with two vector bosons. No significant excess, relative to the Standard Model expectation, is observed and limits on the production cross-section are set at 95% confidence level for a heavy scalar resonance in the context of an extended Higgs sector, and for a non-resonant Standard Model Higgs boson pair production. Interpretation in terms of the coupling between a Higgs boson pair and two vector bosons is also provided.

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

11-JUL-1913126 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

11-JUL-1913139 fb-1Documents | Briefing | Internal
HIGGConference noteH(125)->gammagamma differential cross sectionsFull Title: Measurement of fiducial crosssections in the $H \rightarrow \gamma \gamma$ decay channel with 140 fb$^{-1}$ of 13 TeV proton-proton collision data 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

11-JUL-1913139 fb-1Documents | Briefing | Internal
HIGGConference noteSearch H(125)->mumuFull Title: A search for the dimuon decay of the Standard Model Higgs boson in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS Detector

Abstract: A search for the dimuon decay of the Standard Model Higgs boson is performed using data corresponding to an integrated luminosity of 139 fb$^{-1}$ collected in Run 2 with the ATLAS detector in $pp$ collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider. No significant excess is observed above the expected background. The observed upper limit on the cross section times branching ratio is $1.7$ times the Standard Model prediction at 95% confidence level for a Higgs boson mass of 125.09 GeV, while the expected limit in the absence (assuming SM signal yield) of a $H\to\mu\mu$ signal is $1.3$ ($2.2$). The measured signal strength, defined as the ratio of the observed signal yield to the one expected in the Standard Model, is $\mu = 0.5 \pm 0.7$.

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

11-JUL-1913139 fb-1Documents | Briefing | Internal
SUSYConference noteChargino-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 energy 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, either an electron or 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 $\mathrm{fb}^{-1}$ of $\sqrt{s}=13$ TeV $pp$ collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. No statistically-significant evidence is found for an excess of events above the Standard Model expectation. 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

10-JUL-1913139 fb-1Documents | Internal
HIGGConference noteh(125)->4l STXS and differential cross sectionsFull Title: Measurements of the Higgs boson inclusive, differential and production cross sections in the 4$\ell$ decay channel at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract: Inclusive, differential and production mode cross sections of the Higgs boson are measured in the $H \to ZZ^{*} \to 4\ell$ decay channel. Additionally, cross sections are measured for the main production modes in several exclusive regions of the Higgs boson production phase space. The dataset used corresponds to 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 process $H \to ZZ^{*} \to 4\ell$ is measured to be 3.35 $\pm$ 0.32 fb, while the Standard Model prediction is 3.41 $\pm$ 0.18 fb. The cross-section times $H \to ZZ^{*}$ branching ratio with $|y_H|<$~2.5 for gluon fusion and vector-boson fusion production are measured to be $1.14~ \pm ~0.13~$ pb and $0.13 ~\pm ~0.04~$ pb, respectively. All measurements are in agreement with the Standard Model prediction.

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,VBF,Gluon fusion,Differential measurement,Cross-section measurement,Higgs,ZZ,>=3 leptons

09-JUL-1913139 fb-1Documents | Briefing | Internal
TOPQConference noteMeasurement of ttbar charge asymmetry at 13 TeV in l+jetsFull 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

09-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
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

03-JUN-1913139 fb-1Documents | Internal
SUSYConference noteChargino-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 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-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

19-MAY-1913139 fb-1Documents | Internal
SUSYConference noteChargino-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 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,Higgsino production,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, 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, 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 photonsFull 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 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

17-MAY-1913139 fb-1Documents | Internal
SUSYConference noteStaus; tausFull 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
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 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,Displaced vertex,Stop pair production,Long-lived massive particles,BSM search,Long-lived massive particle,MET,1 lepton

18-MAR-1913136 fb-1Documents | 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

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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