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

The CDF Collaboration

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 t…