TY - JOUR
T1 - Observation of top-quark pair production in association with a photon and measurement of the $t\bar{t}\gamma$ production cross section in pp collisions at $\sqrt{s}=7$ TeV using the ATLAS detector
AU - Clark, Philip James
AU - Leonidopoulos, Christos
AU - Martin, Victoria Jane
AU - Mills, Corrinne
AU - Collaboration, Atlas
PY - 2015/4/28
Y1 - 2015/4/28
N2 - 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 σtt¯γfid×BR=63±8(stat)-13+17(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.
AB - 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 σtt¯γfid×BR=63±8(stat)-13+17(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.
U2 - 10.1103/PhysRevD.91.072007
DO - 10.1103/PhysRevD.91.072007
M3 - Article
SN - 0031-899X
VL - D91
SP - 072007
JO - Physical Review
JF - Physical Review
IS - 7
M1 - Aad:2015uwa
ER -