Measurement of the inclusive t tbar gamma cross section with the ATLAS detector

Top quark pair events with additional photons in the final state are directly sensitive to the t¯tγ vertex. In this note, a first measurement of the t¯tγ cross section in pp collisions at √s = 7 TeV is presented using 1.04 fb−1 of data taken with the ATLAS detector. Events are selected that contain a large transverse momentum electron or muon and a large transverse momentum photon. In the electron and muon samples, 52 and 70 candidate events have been identified, respectively. The resulting cross section times branching ratio into the single lepton and dilepton channels (including τ-leptons) for t ¯tγ production with a photon with transverse momentum above 8 GeV is σ(t¯tγ) = 2.0 ± 0.5 (stat.) ± 0.7 (syst.) ± 0.08 (lumi.) pb, which is consistent with theoretical calculations