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 √s=8 TeV collected by the ATLAS detector at the LHC. No evidence of QQ ¯ 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) .
