Search for pair production of heavy top-like quarks decaying to a high-pT W boson and a b quark in the lepton plus jets final state at s=7TeV with the ATLAS detector

A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search is based on 4.7 fb-1 of pp collisions at s=7TeV recorded in 2011 with 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, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t't??????' signal when mt'?????????400GeV. No significant excess of events above the Standard Model expectation is observed and the result of the search is interpreted in the context of fourth-generation and vector-like quark models. Under the assumption of a branching ratio BR(t'?????????Wb)=1, a fourth-generation t' quark with mass lower than 656GeV is excluded at 95% confidence level. In addition, in light of the recent discovery of a new boson of mass ~126GeV at the LHC, upper limits are derived in the two-dimensional plane of BR(t'?????????Wb) versus BR(t'?????????Ht), where H is the Standard Model Higgs boson, for vector-like quarks of various masses. ?????? 2012 CERN.