Search for pair production of a new $b'$ quark that decays to a $Z$ boson and a bottom quark with the ATLAS detector at the LHC

We report a search for a new down-type quark, denoted $b'$, that is pair produced in $pp$ collisions at $\sqrt{s} = 7$ TeV with at least one $b'$ decaying to a $Z$ boson and a bottom quark. This search complements recent searches for a $b'$ in the $W$ boson plus top quark mode, and is particularly relevant for vector-like quark models. The data comprise 2.0 fb${}^{-1}$ of integrated luminosity collected by the ATLAS detector at the LHC in 2011. From events containing both a Z boson reconstructed from electrons, and a b-tagged jet, we enrich any potential signal by selecting a subsample with large $b'$ candidate $p_T$. We present limits on the mass of the $b'$.