Measurement of the top quark-pair production cross section with ATLAS in pp collisions at √s=7 TeV

A measurement of the production cross-section for top quark pairs (tt) in pp collisions at √s=7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron e or muon μ) with large missing transverse energy and at least four jets, and dilepton (ee, μμ or eμ) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb−1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non- tt Standard Model processes are estimated using data-driven methods and determined to be 12.2±3.9 events and 2.5±0.6 events, respectively. The kinematic properties of the selected events are consistent with SM tt production. The inclusive top quark pair production cross-section is measured to be σt=145±31(stat.)+42−27(syst.) pb. The measurement agrees with perturbative QCD calculations