Search for the production of single vector-like and excited quarks in the $Wt$ final state in $pp$ collisions at $\sqrt{s} =$ 8 TeV with the ATLAS detector

search for vector-like quarks and excited quarks in events containing a top quark and a?W?boson in the final state is reported here. The search is based on?20.3fb?1?of proton--proton collision data taken at the LHC at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector. Events with one or two leptons, and one, two or three jets are selected with the additional requirement that at least one jet contains a?b-quark. Single-lepton events are also required to contain at least one large-radius jet from the hadronic decay of a high-pT?W?boson or a top quark. No significant excess over the expected background is observed and upper limits on the cross-section times branching ratio for different vector-like quark and excited-quark model masses are derived. For the excited-quark production and decay to?Wt?with unit couplings, quarks with masses below 1500 GeV are excluded and coupling-dependent limits are set.