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 (t′) together with its antiparticle, assuming subsequent decay to a W boson and a b quark, t′t̅ ′→W+bW-b̅ . The search is based on 1.04  fb-1 of proton-proton collisions at √s=7  TeV collected by the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton+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 t′ quark.