Observation of top-quark pair production in association with a photon and measurement of the tt¯γ production cross section in pp collisions at √s=7 TeV using the ATLAS detector

Allison, Lee and Barton, Adam and Borissov, Guennadi and Bouhova-Thacker, Eva and Chilingarov, Alexandre and Dearnaley, William and Fox, Harald and Grimm, Kathryn and Henderson, Robert and Hughes, Gareth and Jones, Roger William Lewis and Kartvelishvili, Vakhtang and Long, Robin and Love, Peter and Maddocks, Harvey and Smizanska, Maria and Walder, James (2015) Observation of top-quark pair production in association with a photon and measurement of the tt¯γ production cross section in pp collisions at √s=7 TeV using the ATLAS detector. Physical Review D, 91 (7). ISSN 1550-7998

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Abstract

A search is performed for top-quark pairs (tt¯) produced together with a photon (γ) with transverse energy greater than 20 GeV using a sample of tt¯ 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−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 tt¯γ candidate events are observed in the electron and muon channels, to be compared to the expectation of 79±26 and 120±39 non-tt¯γ background events, respectively. The production of tt¯γ events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The tt¯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 σfidtt¯γ×BR=63±8(stat)+17−13(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.

Item Type:
Journal Article
Journal or Publication Title:
Physical Review D
Additional Information:
© 2015 CERN, for the ATLAS Collaboration
ID Code:
74071
Deposited By:
Deposited On:
18 Jun 2015 06:01
Refereed?:
Yes
Published?:
Published
Last Modified:
10 Jul 2020 03:45