Top-quark pair cross-section measurement in the lepton+jets channel

A measurement of the production cross-section for top quark pairs in $pp$ collisions at $\sqrt{s}$ =7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider (LHC). Events are selected in the lepton+jets topology by requiring a single lepton (electron or muon), large missing transverse energy and at least three jets. No explicit identification of secondary vertices inside jets (b-tagging) is performed. In a data sample of 35.3 $pb^{−1}$ , 2009 and 1181 candidate events are observed in the µ+jets and e+jets topology, respectively. A simple multivariate method using three kinematic variables is employed to extract a cross-section measurement of $171±17(stat.)^{+20}_{−17}$(syst.)±5(lumi.) pb.