Search for Fermion-Pair Decays $Q\Qbar \to (\t\Wmp)(\tbar\Wpm)$ in Same-Charge Dilepton Events

Abstract

We report the most restrictive direct limits on masses of fourth-generation down-type quarks $b^{\prime }$, and quark-like composite fermions ($B$ or $T_{5/3}$), decaying promptly to $t{W}^{\mp }$. We search for a significant excess of events with two same-charge leptons ($e$, $\mu$), several hadronic jets, and missing transverse energy. An analysis of data from $p\overline{p}$ collisions with an integrated luminosity of 2.7 fb${}^{-1}$ collected with the CDF II detector at Fermilab yields no evidence for such a signal, setting mass limits $m_{b^{\prime }},m_B>$ 338 $\mathrm{GeV}/c^2$ and $m_{T_{5/3}}>$ 365 $\mathrm{GeV}/c^2$ at 95% confidence level.

7 pages, 4 figures, for Phys. Rev. Lett

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