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 σtt¯=145±31 (stat. ) +42−27 (syst. ) pb. measurement agrees with perturbative QCD calculations.