Examinando por Autor "Aaboud M."

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  • Miniatura
    Ítem
    Determination of jet calibration and energy resolution in proton–proton collisions at √s=8TeV using the ATLAS detector
    (Springer Science and Business Media Deutschland GmbH, 2020-12) Aaboud M.; Aad G.; Abbott B.; Abdinov O.; Abeloos B.; Abidi S.H; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B.S
    The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton–proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20fb-1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-kt algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton–proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in γ + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum 150GeVenergy resolution is (8.4 ± 0.6) % for pT=100GeV and (23 ± 2) % for pT=20GeV. The calibration scheme for jets with radius parameter R= 1.0 , for which jets receive a dedicated calibration of the jet mass, is also discussed. © 2020, The Author(s).
  • Miniatura
    Ítem
    Measurements of top-quark pair spin correlations in the eμ channel at √s=13 TeV using pp collisions in the ATLAS detector
    (Springer, 2020-08) Aaboud M.; Aad G.; Abbott B.; Abbott D.C.; Abdinov O.; Abud, A. Abed; Abhayasinghe D.K.; Abidi S.H.; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.
    A measurement of observables sensitive to spin correlations in tt¯ production is presented, using 36.1 fb - 1 of pp collision data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the tt¯ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass. © 2020, CERN for the benefit of the ATLAS Collaboration.