Simultaneous energy and mass calibration of large-radius jets with the ATLAS detector using a deep neural network

The energy and mass measurements of jets are crucial tasks for the Large Hadron Collider experiments. This paper presents a new calibration method to simultaneously calibrate these quantities for large-radius jets measured with the ATLAS detector using a deep neural network (DNN). To address the specificities of the calibration problem, special loss functions and training procedures are employed, and a complex network architecture, which includes feature annotation and residual connection layers, is used. The DNN-based calibration is compared to the standard numerical approach in an extensive series of tests. The DNN approach is found to perform significantly better in almost all of the tests and over most of the relevant kinematic phase space. In particular, it consistently improves the energy and mass resolutions, with a 30% better energy resolution obtained for transverse momenta pT > 500 GeV

Search for supersymmetry in final states with missing transverse momentum and three or more b-jets in 139 fb−1^{-1} of proton–proton collisions at s=13\sqrt{s} = 13 TeV with the ATLAS detector

International audienceA search for supersymmetry involving the pair production of gluinos decaying via off-shell third-generation squarks into the lightest neutralino $(\tilde{\chi }^0_1)$ is reported. It exploits LHC proton–proton collision data at a centre-of-mass energy $\sqrt{s} = 13$ TeV with an integrated luminosity of 139 fb$^{-1}$ collected with the ATLAS detector from 2015 to 2018. The search uses events containing large missing transverse momentum, up to one electron or muon, and several energetic jets, at least three of which must be identified as containing b-hadrons. Both a simple kinematic event selection and an event selection based upon a deep neural-network are used. No significant excess above the predicted background is found. In simplified models involving the pair production of gluinos that decay via off-shell top (bottom) squarks, gluino masses less than 2.44 TeV (2.35 TeV) are excluded at 95% CL for a massless $\tilde{\chi }^0_1.$ Limits are also set on the gluino mass in models with variable branching ratios for gluino decays to $b\bar{b}\tilde{\chi }^0_1,t\bar{t}\tilde{\chi }^0_1$ and $t\bar{b}\tilde{\chi }^-_1/\bar{t}b\tilde{\chi }^+_1.

Search for pair production of third-generation leptoquarks decaying into a bottom quark and a τ\tau -lepton with the ATLAS detector

International audienceA search for pair-produced scalar or vector leptoquarks decaying into a b-quark and a $\tau$-lepton is presented using the full LHC Run 2 (2015–2018) data sample of 139 fb$^{-1}$ collected with the ATLAS detector in proton–proton collisions at a centre-of-mass energy of $\sqrt{s} =13$ TeV. Events in which at least one $\tau$-lepton decays hadronically are considered, and multivariate discriminants are used to extract the signals. No significant deviations from the Standard Model expectation are observed and 95% confidence-level upper limits on the production cross-section are derived as a function of leptoquark mass and branching ratio $\mathcal {B}$ into a $\tau$-lepton and b-quark. For scalar leptoquarks, masses below 1460 GeV are excluded assuming $\mathcal {B}=100$%, while for vector leptoquarks the corresponding limit is 1650 GeV (1910 GeV) in the minimal-coupling (Yang–Mills) scenario

Search for pair production of third-generation leptoquarks decaying into a bottom quark and a τ\tau-lepton with the ATLAS detector

A search for pair-produced scalar or vector leptoquarks decaying into a $b$-quark and a $\tau$-lepton is presented using the full LHC Run 2 (2015-2018) data sample of 139 fb$^{-1}$ collected with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV. Events in which at least one $\tau$-lepton decays hadronically are considered, and multivariate discriminants are used to extract the signals. No significant deviations from the Standard Model expectation are observed and 95% confidence-level upper limits on the production cross-section are derived as a function of leptoquark mass and branching ratio into the $\tau$-lepton. For scalar leptoquarks, masses below 1490 GeV are excluded assuming a 100% branching ratio, while for vector leptoquarks the corresponding limit is 1690 GeV (1960 GeV) in the minimal-coupling (Yang-Mills) scenario.A search for pair-produced scalar or vector leptoquarks decaying into a $b$-quark and a $\tau$-lepton is presented using the full LHC Run 2 (2015-2018) data sample of 139 fb$^{-1}$ collected with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV. Events in which at least one $\tau$-lepton decays hadronically are considered, and multivariate discriminants are used to extract the signals. No significant deviations from the Standard Model expectation are observed and 95% confidence-level upper limits on the production cross-section are derived as a function of leptoquark mass and branching ratio into the $\tau$-lepton. For scalar leptoquarks, masses below 1490 GeV are excluded assuming a 100% branching ratio, while for vector leptoquarks the corresponding limit is 1690 GeV (1960 GeV) in the minimal-coupling (Yang-Mills) scenario

Search for leptonic charge asymmetry in tt‾W t\overline{t}W production in final states with three leptons at s \sqrt{s} = 13 TeV

International audienceA search for the leptonic charge asymmetry (${A}_{\textrm{c}}^{\ell }$) of top-quark-antiquark pair production in association with a W boson ($t\overline{t}W$) is presented. The search is performed using final states with exactly three charged light leptons (electrons or muons) and is based on $\sqrt{s}$ = 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN during the years 2015–2018, corresponding to an integrated luminosity of 139 fb$^{−1}$. A profile-likelihood fit to the event yields in multiple regions corresponding to positive and negative differences between the pseudorapidities of the charged leptons from top-quark and top-antiquark decays is used to extract the charge asymmetry. At reconstruction level, the asymmetry is found to be −0.12 ± 0.14 (stat.) ± 0.05 (syst.). An unfolding procedure is applied to convert the result at reconstruction level into a charge-asymmetry value in a fiducial volume at particle level with the result of −0.11 ± 0.17 (stat.) ± 0.05 (syst.). The Standard Model expectations for these two observables are calculated using Monte Carlo simulations with next-to-leading-order plus parton shower precision in quantum chromodynamics and including next-to-leading-order electroweak corrections. They are $-{0.084}_{-0.003}^{+0.005}$ (scale) ± 0.006 (MC stat.) and $-{0.063}_{-0.004}^{+0.007}$ (scale) ± 0.004 (MC stat.) respectively, and in agreement with the measurements.[graphic not available: see fulltext

Search for long-lived, massive particles in events with displaced vertices and multiple jets in pp collisions at s \sqrt{s} = 13 TeV with the ATLAS detector

International audienceA search for long-lived particles decaying into hadrons is presented. The analysis uses 139 fb$^{−1}$ of pp collision data collected at $\sqrt{s}$ = 13 TeV by the ATLAS detector at the LHC using events that contain multiple energetic jets and a displaced vertex. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particles decaying in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are used to set limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and on scenarios with pair-production of supersymmetric particles with long-lived electroweakinos that decay via a small R-parity-violating coupling. The pair-production of electroweakinos with masses below 1.5 TeV is excluded for mean proper lifetimes in the range from 0.03 ns to 1 ns. When produced in the decay of $m\left(\overset{\sim }{g}\right)$ = 2.4 TeV gluinos, electroweakinos with $m\left({\overset{\sim }{\chi}}_1^0\right)$ = 1.5 TeV are excluded with lifetimes in the range of 0.02 ns to 4 ns.[graphic not available: see fulltext

Luminosity determination in pppp collisions at s=13\sqrt{s}=13 TeV using the ATLAS detector at the LHC

The luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with $pp$ collisions at $\sqrt{s}=13$ TeV. The absolute luminosity scale is determined using van der Meer beam separation 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 in the integrated luminosities for each individual year of data-taking range from 0.9% to 1.1%, and are partially correlated between years. After standard data-quality selections, the full Run 2 $pp$ data sample corresponds to an integrated luminosity of $140.1\pm 1.2$ fb$^{-1}$, i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017-18 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of $338.1\pm 3.1$ pb$^{-1}$.The luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with pp collisions at a centre-of-mass energy $\sqrt{s}=13$ TeV. The absolute luminosity scale is determined using van der Meer beam separation 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 in the integrated luminosity for each individual year of data-taking range from 0.9% to 1.1%, and are partially correlated between years. After standard data-quality selections, the full Run 2 pp data sample corresponds to an integrated luminosity of $140.1\pm 1.2$ $\hbox {fb}^{-1}$, i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017–2018 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of $338.1\pm 3.1$ $\hbox {pb}^{-1}$.The luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with $pp$ collisions at $\sqrt{s}=13$ TeV. The absolute luminosity scale is determined using van der Meer beam separation 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 in the integrated luminosities for each individual year of data-taking range from 0.9% to 1.1%, and are partially correlated between years. After standard data-quality selections, the full Run 2 $pp$ data sample corresponds to an integrated luminosity of $140.1\pm 1.2$ fb$^{-1}$, i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017-18 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of $338.1\pm 3.1$ pb$^{-1}$