Search for Down-Type Fourth Generation Quarks with the ATLAS Detector in Events with One Lepton and Hadronically Decaying<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>W</mml:mi></mml:math>Bosons

Abstract

This Letter presents a search for pair production of heavy down-type quarks decaying via ${b}^{\ensuremath{'}}\ensuremath{\rightarrow}Wt$ in the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ channel, as ${b}^{\ensuremath{'}}{\overline{b}}^{\ensuremath{'}}\ensuremath{\rightarrow}{W}^{\ensuremath{-}}t{W}^{+}\overline{t}\ensuremath{\rightarrow}b\overline{b}{W}^{+}{W}^{\ensuremath{-}}{W}^{+}{W}^{\ensuremath{-}}\ensuremath{\rightarrow}{l}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\nu}b\overline{b}q\overline{q}q\overline{q}q\overline{q}$. In addition to requiring exactly one lepton, large missing transverse momentum, and at least six jets, the invariant mass of nearby jet pairs is used to identify high transverse momentum $W$ bosons. In data corresponding to an integrated luminosity of $1.04\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ from $pp$ collisions at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ recorded with the ATLAS detector, a heavy down-type quark with mass less than 480 GeV can be excluded at the 95% confidence level.