Search for resonant top quark plus jet production in tt[over ¯]+jets events with the ATLAS detector in pp collisions at √s=7 TeV

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 tq or tq, leading to a resonance within the tt þ jets signature. The full 2011
ATLAS pp collision data set from the LHC (4:7 fb1) is used to search for tt 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 W0 boson and color triplet models is excluded at 95% confidence level,
assuming unit right-handed coupling.