We measure the t¯t production cross section in p¯p collisions at √s=1.96 TeV in the lepton+jets channel. Two complementary methods discriminate between signal and background: b tagging and a kinematic likelihood discriminant. Based on 0.9 fb−1 of data collected by the D0 detector at the Fermilab Tevatron Collider, we measure σt¯t=7.62±0.85 pb, assuming the current world average mt=172.6 GeV. We compare our cross section measurement with theory predictions to determine a value for the top-quark mass of 170±7 GeV.Received 19 March 2008DOI:https://doi.org/10.1103/PhysRevLett.100.192004©2008 American Physical Society