Search for Pair Production of a New Heavy Quark that Decays into a W Boson and a Light Quark in pp Collisions at √s̅ =8 TeV with the ATLAS Detector

A search is presented for pair production of a new heavy quark (Q) that decays into a W boson and a light quark (q) in the final state where one W boson decays leptonically (to an electron or muon plus a neutrino) and the other W boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb⁻¹ of pp collisions at √s̅ = 8 TeV collected by the ATLAS detector at the LHC. No evidence of QQ̅ production is observed. New chiral quarks with masses below 690 GeV are excluded at 95% confidence level, assuming BR(Q → Wq) = 1. Results are also interpreted in the context of vectorlike quark models, resulting in the limits on the mass of a vectorlike quark in the two-dimensional plane of BR(Q → Wq) versus BR(Q → Hq).