Measurement of the ttbar production cross-section in pp collisions at sqrt{s} = 7 TeV using kinematic information of lepton+jets events

A measurement of the ttbar production cross section in pp collisions at a center-of-mass energy of sqrt{s}=7 TeV is presented. The analyzed data consists of candidate events with one charged lepton (electron or muon), large transverse momentum imbalance and at least three jets and correspond to the ingerated luminosity of 698/pb recorded by the ATLAS detector at the Large Hadron Collider. The ttbar signal is distinguished from the background by utilizing the difference in kinematics between ttbar signal and dominant W+jets background events and constructing a discriminant. Cross section is extracted from the fit of the discriminant distribution to data with systematic uncertainties included into the fit. For a top quark mass of 172.5 GeV, the measured cross section yields σ(t¯t) = 179.0 +9.8−9.7 (stat+syst) ± 6.6(lumi) pb in agreement with approximate NNLO perturbative QCD calculations.