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

Abstract

A measurement of the production cross-section for top quark pairs($ttbar$) in $pp$ collisions at $sqrt{s}=7 TeV$ 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 $mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $mumu$ or $emu$) 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-$ttbar$ Standard Model processes are estimated using data-driven methods and determined to be $12.2 pm 3.9$ events and $2.5 pm 0.6$ events, respectively. The kinematic properties of the selected events are consistent with SM $ttbar$ production. The inclusive top quark pair production cross-section is measured to be $sigmattbar=145 pm 31 ^{_s1642}_{-27}$ pb where the first uncertainty is statistical and the second systematic. The measurement agrees with perturbative QCD calculations.