Searches for vector-like quarks and top-jet resonances with ATLAS

Three distinct analyses, based on data collected in 2011 by the ATLAS detector with an LHC energy of √s = 7 TeV are summarized in the following proceedings. The first involves the search for pair production of vector-like quark singlets (VLS) b′ decaying by neutral current b′ → Zb. With 1.98 fb−1 of integrated luminosity, and using events with a least one b-tagged jet and a Z boson reconstructed from a pair of opposite sign electrons, a 95% confidence level exclusion is obtained for masses m(b′ ) < 400 GeV, assuming that the VLS decays entirely to Z + b. The second analysis discussed is the search for single production of vector-like quarks coupling to light generations. With 1.04 fb−1 of integrated luminosity, both the charged current (CC) and (NC) processes, pp → Qq → Wqq′ and pp → Qq → Wqq′ with leptonic decays of the vector gauge bosons were analysed. No evidence of heavy vector-like quarks is observed above the Standard Model expectation. For a coupling κQq = v/mQ, where v is the Higgs vacuum expectation value, limits of 900 GeV and 760 GeV are obtained in the CC and NC channels respectively at 95% confidence level. Finally, the third analysis presented here is a search for a new particle X produced singly in associated with a t(t ̄) quark and decaying to a t ̄(t) quark and a light quark. Using the full 2011 LHC luminosity of 4.7 fb−1, the data are found to be in agreement with Standard Model expectation. At 95% confidence level, X masses below 350 (430) GeV for color singlet (triplet) resonances are excluded assuming a right-handed coupling.