Abstract
A measurement of the top quark pair-production cross section in the lepton þ jets decay channel is
presented. It is based on 4.6 fb−1 of √s= 7 TeV pp collision data collected during 2011 by the ATLAS
experiment at the CERN Large Hadron Collider. A three-class, multidimensional event classifier based on
support vector machines is used to differentiate t ̄t events from backgrounds. The t ̄t production cross section
is found to be σ ̄ 1⁄4 168.5 0.7ðstatÞ þ6.2 ðsystÞ þ3.4 ðlumiÞ pb. The result is consistent with the Standard tt −5.9 −3.2
Model prediction based on QCD calculations at next-to-next-to-leading order.