Search for Pair Production of a New<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>b</mml:mi><mml:mo>′</mml:mo></mml:msup></mml:math>Quark that Decays into a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Z</mml:mi></mml:math>Boson and a Bottom Quark with the ATLAS Detector

A search is reported for the pair production of a new quark ${b}^{\ensuremath{'}}$ with at least one ${b}^{\ensuremath{'}}$ decaying to a $Z$ boson and a bottom quark. The data, corresponding to $2.0\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity, were collected from $pp$ collisions at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ with the ATLAS detector at the CERN Large Hadron Collider. Using events with a $b$-tagged jet and a $Z$ boson reconstructed from opposite-charge electrons, the mass distribution of large transverse momentum ${b}^{\ensuremath{'}}$ candidates is tested for an enhancement. No evidence for a ${b}^{\ensuremath{'}}$ signal is detected in the observed mass distribution, resulting in the exclusion at a 95% confidence level of ${b}^{\ensuremath{'}}$ quarks with masses ${m}_{{b}^{\ensuremath{'}}}<400\text{ }\text{ }\mathrm{GeV}$ that decay entirely via ${b}^{\ensuremath{'}}\ensuremath{\rightarrow}Z+b$. In the case of a vectorlike singlet ${b}^{\ensuremath{'}}$ mixing solely with the third standard model generation, masses ${m}_{{b}^{\ensuremath{'}}}<358\text{ }\text{ }\mathrm{GeV}$ are excluded.

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