  This paper presents a search for a new heavy particle produced in association
with a top or antitop quark. Two models in which the new heavy particle is a
color singlet or a color triplet are considered, decaying respectively to tbarq
or tq, leading to a resonance within the ttbar + jets signature. The full 2011
ATLAS pp collision dataset from the LHC (4.7 fb-1) is used to search for ttbar
events produced in association with jets, in which one of the W bosons from the
top quarks decays leptonically and the other decays hadronically. The data are
consistent with the Standard Model expectation, and a new particle with mass
below 430 GeV for both W boson and color triplet models is excluded at 95%
confidence level, assuming unit right-handed coupling.
