Differential top–antitop cross-section measurements as a function of observables constructed from final-state particles using pp collisions at √s=7 TeV in the ATLAS detector

Aad, G. and Abbott, B. and Abdallah, J. and Abdel, Khalek S. and Abdinov, O. and Krasznahorkay, Attila and Nagai, Yoshikazu and Pásztor, Gabriella and Tóth, József (2015) Differential top–antitop cross-section measurements as a function of observables constructed from final-state particles using pp collisions at √s=7 TeV in the ATLAS detector. JOURNAL OF HIGH ENERGY PHYSICS (6). ISSN 1126-6708

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Abstract

Various differential cross-sections are measured in top-quark pair (t¯t) events produced in proton– proton collisions at a centre-of-mass energy of √s = 7 TeV at the LHC with the ATLAS detector. These differential cross-sections are presented in a data set corresponding to an integrated lumi- nosity of 4.6 fb−1. The differential cross-sections are presented in terms of kinematic variables of a top-quark proxy referred to as the pseudo-top-quark whose dependence on theoretical models is minimal. The pseudo-top-quark can be defined in terms of either reconstructed detector objects or stable particles in an analogous way. The measurements are performed on t¯t events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a b-quark. The hadronic and leptonic pseudo-top-quarks are defined via the lep- tonic or hadronic decay mode of the W boson produced by the top-quark decay in events with a single charged lepton. The cross-section is measured as a function of the transverse momentum and rapidity of both the hadronic and leptonic pseudo-top-quark as well as the transverse momentum, rapidity and invariant mass of the pseudo-top-quark pair system. The measurements are corrected for detector effects and are presented within a kinematic range that closely matches the detector acceptance. Dif- ferential cross-section measurements of the pseudo-top-quark variables are compared with several Monte Carlo models that implement next-to-leading order or leading-order multi-leg matrix-element calculations.

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