Observation of top-quark pair production in association with a photon and measurement of the t[bar over t]γ production cross section in pp collisions at √s = 7 TeV using the ATLAS detector
Author(s)Taylor, Frank E.
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A search is performed for top-quark pairs (t[bar over t]) produced together with a photon (γ) with transverse energy greater than 20 GeV using a sample of t[bar over t] candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 fb[superscript −1] of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 t[bar over t]γ candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 ± 26 and 120 ± 39 non-t[bar over t]γ background events, respectively. The production of t[bar over t]γ events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The t[bar over t]γ production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is σ[fid over t[bar over t]γ] × BR = 63 ± 8(stat)[+17 over −13](syst) ± 1(lumi) fb per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of 48 ± 10 fb.
DepartmentMassachusetts Institute of Technology. Department of Physics
Physical Review D
American Physical Society
Aad, G., B. Abbott, J. Abdallah, S. Abdel Khalek, O. Abdinov, R. Aben, B. Abi, et al. "Observation of Top-Quark Pair Production in Association with a Photon and Measurement of the t[bar over t]γ Production Cross Section in pp Collisions at √s = 7 TeV Using the ATLAS Detector.” Phys. Rev. D 91, no. 7 (April 2015). © 2015 CERN, for the ATLAS Collaboration
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