14 research outputs found

    Search for lepton-flavor violation in different-flavor, high-mass final states in pp collisions at √s=13 TeV with the ATLAS detector

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    A search is performed for a heavy particle decaying into different-flavor, dilepton pairs (eμ, eτ or μτ), using 36.1  fb−1 of proton-proton collision data at √s=13  TeV collected in 2015–2016 by the ATLAS detector at the Large Hadron Collider. No excesses over the Standard Model predictions are observed. Bayesian lower limits at the 95% credibility level are placed on the mass of a Z′ boson, the mass of a supersymmetric τ-sneutrino, and on the threshold mass for quantum black-hole production. For the Z′ and sneutrino models, upper cross-section limits are converted to upper limits on couplings, which are compared with similar limits from low-energy experiments and which are more stringent for the eτ and μτ modes

    Search for lepton-flavor-violating decays of the Z boson into a τ lepton and a light lepton with the ATLAS detector

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    For abstract see published article

    Search for resonances in the mass distribution of jet pairs with one or two jets identified as b-jets in proton-proton collisions at √s = 13 TeV with the ATLAS detector

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    A search for new resonances decaying into jets containing b -hadrons in p p collisions with the ATLAS detector at the LHC is presented in the dijet mass range from 0.57 to 7 TeV. The data set corresponds to an integrated luminosity of up to 36.1     fb − 1 collected in 2015 and 2016 at √ s = 13     TeV . No evidence of a significant excess of events above the smooth background shape is found. Upper cross-section limits and lower limits on the corresponding signal mass parameters for several types of signal hypotheses are provided at 95% C.L. In addition, 95% C.L. upper limits are set on the cross sections for new processes that would produce Gaussian-shaped signals in the di- b -jet mass distributions

    Search for resonances in the mass distribution of jet pairs with one or two jets identified as b-jets in proton-proton collisions at √s = 13 TeV with the ATLAS detector

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    A search for new resonances decaying into jets containing b -hadrons in p p collisions with the ATLAS detector at the LHC is presented in the dijet mass range from 0.57 to 7 TeV. The data set corresponds to an integrated luminosity of up to 36.1     fb − 1 collected in 2015 and 2016 at √ s = 13     TeV . No evidence of a significant excess of events above the smooth background shape is found. Upper cross-section limits and lower limits on the corresponding signal mass parameters for several types of signal hypotheses are provided at 95% C.L. In addition, 95% C.L. upper limits are set on the cross sections for new processes that would produce Gaussian-shaped signals in the di- b -jet mass distributions

    Search for Higgs boson decays into a pair of pseudoscalar particles in the bbμμ final state with the ATLAS detector in pp collisions at √s = 13 TeV

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    This paper presents a search for decays of the Higgs boson with a mass of 125 GeV into a pair of new pseudoscalar particles, H → a a , where one a -boson decays into a b -quark pair and the other into a muon pair. The search uses 139     fb − 1 of proton-proton collision data at a center-of-mass energy of √ s = 13     TeV recorded between 2015 and 2018 by the ATLAS experiment at the LHC. A narrow dimuon resonance is searched for in the invariant mass spectrum between 16 GeV and 62 GeV. The largest excess of events above the Standard Model backgrounds is observed at a dimuon invariant mass of 52 GeV and corresponds to a local (global) significance of 3.3 σ ( 1.7 σ ). Upper limits at 95% confidence level are placed on the branching ratio of the Higgs boson to the b b μ μ final state, B ( H → a a → b b μ μ ) , and are in the range 0.2 – 4.0 × 10 − 4 , depending on the signal mass hypothesis

    The Financial Policy in the Later Meiji Era

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    A search for resonant and nonresonant pair production of Higgs bosons in the b¯bτ+τ− final state is presented. The search uses 36.1  fb−1 of pp collision data with √s=13  TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. Decays of the τ-lepton pairs with at least one τ lepton decaying to final states with hadrons and a neutrino are considered. No significant excess above the expected background is observed in the data. The cross-section times branching ratio for nonresonant Higgs boson pair production is constrained to be less than 30.9 fb, 12.7 times the standard model expectation, at 95% confidence level. The data are also analyzed to probe resonant Higgs boson pair production, constraining a model with an extended Higgs sector based on two doublets and a Randall-Sundrum bulk graviton model. Upper limits are placed on the resonant Higgs boson pair production cross-section times branching ratio, excluding resonances X in the mass range 305  GeV<mX<402  GeV in the simplified hMSSM minimal supersymmetric model for tanβ=2 and excluding bulk Randall-Sundrum gravitons GKK in the mass range 325  GeV<mGKK<885  GeV for k/¯MPl=1

    Measurement of ZZ production in the ℓℓνν final state with the ATLAS detector in pp collisions at s = 13 TeV

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    Abstract: This paper presents a measurement of ZZ production with the ATLAS detector at the Large Hadron Collider. The measurement is carried out in the final state with two charged leptons and two neutrinos, using data collected during 2015 and 2016 in pp collisions at s = 13 TeV, corresponding to an integrated luminosity of 36.1 fb−1. The integrated cross-sections in the total and fiducial phase spaces are measured with an uncertainty of 7% and compared with Standard Model predictions, and differential measurements in the fiducial phase space are reported. No significant deviations from the Standard Model predictions are observed, and stringent constraints are placed on anomalous couplings corresponding to neutral triple gauge-boson interactions

    Measurement of ZZ production in the ℓℓνν final state with the ATLAS detector in pp collisions at s \sqrt{s} = 13 TeV

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    Abstract This paper presents a measurement of ZZ production with the ATLAS detector at the Large Hadron Collider. The measurement is carried out in the final state with two charged leptons and two neutrinos, using data collected during 2015 and 2016 in pp collisions at s \sqrt{s} s = 13 TeV, corresponding to an integrated luminosity of 36.1 fb −1. The integrated cross-sections in the total and fiducial phase spaces are measured with an uncertainty of 7% and compared with Standard Model predictions, and differential measurements in the fiducial phase space are reported. No significant deviations from the Standard Model predictions are observed, and stringent constraints are placed on anomalous couplings corresponding to neutral triple gauge-boson interactions.</jats:p

    Measurements of sensor radiation damage in the ATLAS inner detector using leakage currents

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    Non-ionizing energy loss causes bulk damage to the silicon sensors of the ATLAS pixel and strip detectors. This damage has important implications for data-taking operations, charged-particle track reconstruction, detector simulations, and physics analysis. This paper presents simulations and measurements of the leakage current in the ATLAS pixel detector and semiconductor tracker as a function of location in the detector and time, using data collected in Run 1 (2010-2012) and Run 2 (2015-2018) of the Large Hadron Collider. The extracted fluence shows a much stronger vertical bar z vertical bar-dependence in the innermost layers than is seen in simulation. Furthermore, the overall fluence on the second innermost layer is significantly higher than in simulation, with better agreement in layers at higher radii. These measurements are important for validating the simulation models and can be used in part to justify safety factors for future detector designs and interventions
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