UC Santa Cruz

A measurement of the production cross-section for top quark pairs (tt̅) in pp collisions at √s =7 TeVis 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-tt̅ 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 tt̅ production. The inclusive top quark pair production cross-section is measured to be The measurement agrees with perturbative QCD calculations.