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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Measurement of VH, H -> b(b)over-barproduction as a function of the vector-boson transverse momentum in 13 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 05(5), 141–36pp.
Abstract: Cross-sections of associated production of a Higgs boson decaying into bottomquark 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.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Search for scalar resonances decaying into mu(+)mu(-) in events with and without b-tagged jets produced in proton-proton collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 117–41pp.
Abstract: A search for a narrow scalar resonance decaying into an opposite-sign muon pair produced in events with and without b-tagged jets is presented in this paper. The search uses 36.1 fb(-1) of =13 TeV proton-proton collision data recorded by the ATLAS experiment at the LHC. No significant excess of events above the expected Standard Model background is observed in the investigated mass range of 0.2 to 1.0 TeV. The observed upper limits at 95% confidence level on the cross section times branching ratio for b-quark associated production and gluon-gluon fusion are between 1.9 and 41 fb and 1.6 and 44 fb respectively, which is consistent with expectations.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Search for chargino and neutralino production in final states with a Higgs boson and missing transverse momentum at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 100(1), 012006–37pp.
Abstract: A search is conducted for the electroweak pair production of a chargino and a neutralino pp -> (chi) over tilde (+/-)(1)(chi) over tilde (0)(2), where the chargino decays into the lightest neutralino and a W boson, (chi) over tilde (+/-)(1) -> (chi) over tilde W-0(1)+/- while the neutralino decays into the lightest neutralino and a Standard Model-like 125 GeV Higgs boson,(chi) over tilde (0)(2) -> (chi) over tilde (0)(1)h. Fully hadronic, semileptonic, diphoton, and multilepton (electrons, muons) final. states with missing transverse momentum are considered in this search. Higgs bosons in the final state are identified by either two jets originating from bottom quarks (h -> b (b) over bar), two photons (h -> gamma gamma), or leptons from the decay modes h -> WW, h -> ZZ or h -> tau tau. The analysis is based on 36.1 fb(-1) of s root s = 13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider. Observations are consistent with the Standard Model expectations, and 95% confidence-level limits of up to 680 GeV in (chi) over tilde (+/-)(1)/(chi) over tilde (0)(2) mass are set in the context of a simplified supersymmetric model.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Measurement of ZZ production in the ll nu nu final state with the ATLAS detector in pp collisions at root s=13 TeV. J. High Energy Phys., 10(10), 127–48pp.
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 root 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.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2020). Transverse momentum and process dependent azimuthal anisotropies in root S-NN=8.16 TeV p plus Pb collisions with the ATLAS detector. Eur. Phys. J. C, 80(1), 73–31pp.
Abstract: The azimuthal anisotropy of charged particles produced in sNN=8.16TeV p+Pb collisions is measured with the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 165 nb-1 that was collected in 2016. Azimuthal anisotropy coefficients, elliptic v2 and triangular v3\, extracted using two-particle correlations with a non-flow template fit procedure, are presented as a function of particle transverse momentum (pT) between 0.5 and 50 GeV. The v2 results are also reported as a function of centrality in three different particle pTintervals. The results are reported from minimum-bias events and jet-triggered events, where two jet pT thresholds are used. The anisotropies for particles with pT less than about 2 GeV are consistent with hydrodynamic flow expectations, while the significant non-zero anisotropies for pT in the range 9-50 GeV are not explained within current theoretical frameworks. In the pTrange 2-9 GeV, the anisotropies are larger in minimum-bias than in jet-triggered events. Possible origins of these effects, such as the changing admixture of particles from hard scattering and the underlying event, are discussed.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., Carrio Argos, F., et al. (2018). Operation and performance of the ATLAS Tile Calorimeter in Run 1. Eur. Phys. J. C, 78(12), 987–48pp.
Abstract: The Tile Calorimeter is the hadron calorimeter covering the central region of the ATLAS experiment at the Large Hadron Collider. Approximately 10,000 photomultipliers collect light from scintillating tiles acting as the active material sandwiched between slabs of steel absorber. This paper gives an overview of the calorimeter's performance during the years 2008-2012 using cosmic-ray muon events and proton-proton collision data at centre-of-mass energies of 7 and 8 TeV with a total integrated luminosity of nearly 30 fb(-1). The signal reconstruction methods, calibration systems as well as the detector operation status are presented. The energy and time calibration methods performed excellently, resulting in good stability of the calorimeter response under varying conditions during the LHC Run 1. Finally, the Tile Calorimeter response to isolated muons and hadrons as well as to jets from proton-proton collisions is presented. The results demonstrate excellent performance in accord with specifications mentioned in the Technical Design Report.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Search for supersymmetry in events with four or more charged leptons in 139 fb(-1) of root s=13 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 07(7), 167–57pp.
Abstract: A search for supersymmetry in events with four or more charged leptons (electrons, muons and tau-leptons) is presented. The analysis uses a data sample corresponding to 139 fb(-1) of proton-proton collisions delivered by the Large Hadron Collider at root s = 13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying tau-leptons are designed to target several supersymmetric models, while a general five-lepton signal region targets any new physics phenomena leading to a final state with five charged leptons. Data yields are consistent with Standard Model expectations and results are used to set upper limits on contributions from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge-mediated supersymmetry, excluding higgsino masses up to 540 GeV. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1.6 TeV, 1.2 TeV, and 2.5 TeV are placed on wino, slepton and gluino masses, respectively.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Configuration and performance of the ATLAS b-jet triggers in Run 2. Eur. Phys. J. C, 81(12), 1087–45pp.
Abstract: Several improvements to the ATLAS triggers used to identify jets containing b-hadrons (b-jets) were implemented for data-taking during Run 2 of the Large Hadron Collider from 2016 to 2018. These changes include reconfiguring the b-jet trigger software to improve primary-vertex finding and allow more stable running in conditions with high pile-up, and the implementation of the functionality needed to run sophisticated taggers used by the offline reconstruction in an online environment. These improvements yielded an order of magnitude better light-flavour jet rejection for the same b-jet identification efficiency compared to the performance in Run 1 (2011-2012). The efficiency to identify b-jets in the trigger, and the conditional efficiency for b-jets that satisfy offline b-tagging requirements to pass the trigger are also measured. Correction factors are derived to calibrate the b-tagging efficiency in simulation to match that observed in data. The associated systematic uncertainties are substantially smaller than in previous measurements. In addition, b-jet triggers were operated for the first time during heavy-ion data-taking, using dedicated triggers that were developed to identify semileptonic b-hadron decays by selecting events with geometrically overlapping muons and jets.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo Gimenez, V., et al. (2022). The ATLAS inner detector trigger performance in pp collisions at 13 TeV during LHC Run 2. Eur. Phys. J. C, 82(3), 206–57pp.
Abstract: The design and performance of the inner detector trigger for the high level trigger of the ATLAS experiment at the Large Hadron Collider during the 2016-2018 data taking period is discussed. In 2016, 2017, and 2018 the ATLAS detector recorded 35.6 fb(-1), 46.9 fb(-1), and 60.6 fb(-1) respectively of proton-proton collision data at a centre-of-mass energy of 13TeV. In order to deal with the very high interaction multiplicities per bunch crossing expected with the 13TeV collisions the inner detector trigger was redesigned during the long shutdown of the Large Hadron Collider from 2013 until 2015. An overview of these developments is provided and the performance of the tracking in the trigger for the muon, electron, tau and b-jet signatures is discussed. The high performance of the inner detector trigger with these extreme interaction multiplicities demonstrates how the inner detector tracking continues to lie at the heart of the trigger performance and is essential in enabling the ATLAS physics programme.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., et al. (2020). Measurement of the Z(-> l(+)l(-))gamma production cross-section in pp collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 03(3), 054–52pp.
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 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 from 2015 to 2018. The production cross-section for the process pp -> l(+)l(-)gamma + X (l = e, mu) is measured within a fiducial phase-space region defined by kinematic requirements on the photon and the leptons, and by isolation requirements on the photon. An experimental precision of 2.9% is achieved for the fiducial cross-section. Differential cross-sections are measured as a function of each of six kinematic variables characterising the l(+)l(-)gamma system. The data are compared with theoretical predictions based on next-to-leading-order and next-to-next-to-leading-order perturbative QCD calculations. The impact of next-to-leading-order electroweak corrections is also considered.
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