Measurement of the inclusive ttgamma cross section at sqrt(s) = 7 TeV with the ATLAS detector

Abstract

A first measurement of the ttgamma cross section in pp collisions at the LHC using 1.04 fb^-1 of data taken with the ATLAS detector is presented. A total of 122 candidate events were identified in the single electron and single muon channels. The contributions from background processes with prompt photons, and with electrons or hadrons misidentified as photons were estimated reducing the dependence on simulations by the use of data-driven techniques. The resulting cross section times branching ratio into the single lepton and dilepton decay channels for photons with pt > 8 GeV reads \sigma_ttgamma * BR = 1.9 pm 0.5 (stat.) pm 0.8 (syst.) pm 0.1 (lumi.) pb, which is consistent with the Standard Model expectation from theoretical calculations. The significance of the ttgamma signal was estimated to 2.5 \sigma.