Search for Pair Production of a Heavy Up-Type Quark Decaying to a W Boson and a b Quark in the lepton + jets Channel with the ATLAS Detector

A search is presented for production of a heavy up-type quark (t0) together with its antiparticle, assuming subsequent decay to a W boson and a b quark, t0 t0 ! WþbW b. The search is based on 1:04 fb1 of proton-proton collisions at pffisffiffi ¼ 7 TeV collected by the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton þ jets final state, characterized by a high transverse momentum isolated electron or muon, high missing transverse momentum, and at least three jets. No significant excess of events above the background expectation is observed. A 95% C.L. lower limit of 404 GeV is set for the mass of the t0 quark.