Aaboud, M.Albert, JustinChiu, Y. H.Elliot, Alison A.Fincke-Keeler, J.Hamano, KenjiHill, Ewan ChinKeeler, RichardKowalewski, RobertKuwertz, E. S.Kwan, TonyLeBlanc, Matthew EdgarLefebvre, MichelMcPherson, Robert A.Seuster, RolfSobie, Randall J.Trovatelli, M.Venturi, M.et al.2019-10-172019-10-1720172017The ATLAS collaboration; Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B. … & Zwalinski, L. (2017). Measurement of the t(t)over-bar gamma production cross section in proton-proton collisions at root s=8 TeV with the ATLAS detector. Journal of High Energy Physics, 2017(11), article 86. DOI: 10.1007/JHEP11(2017)086https://doi.org/10.1007/JHEP11(2017)086http://hdl.handle.net/1828/11252The cross section of a top-quark pair produced in association with a photon is measured in proton-proton collisions at a centre-of-mass energy of root s = 8 TeV with 20.2 fb(-1) of data collected by the ATLAS detector at the Large Hadron Collider in 2012. The measurement is performed by selecting events that contain a photon with transverse momentum p(T) > 15 GeV, an isolated lepton with large transverse momentum, large missing transverse momentum, and at least four jets, where at least one is identified as originating from a b-quark. The production cross section is measured in a fiducial region close to the selection requirements. It is found to be 139 +/- 7 (stat.) +/- 17 (syst.) fb, in good agreement with the theoretical prediction at next-to-leading order of 151 +/- 24 fb. In addition, differential cross sections in the fiducial region are measured as a function of the transverse momentum and pseudorapidity of the photon.enHadron-Hadron scattering (experiments)Top physicsArticle