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

TL;DR

This paper sets new lower mass limits on hypothetical fourth-generation quarks and quark-like fermions by searching for same-charge dilepton events in proton-antiproton collision data, with no evidence of such particles found.

Contribution

It provides the most restrictive direct limits on masses of certain hypothetical heavy quarks decaying to top and W bosons, using a novel analysis of same-charge dilepton events.

Findings

No evidence for fourth-generation quarks or fermions in the data.

Mass limits set at 338 GeV/c^2 for $b'$ and $B$, 365 GeV/c^2 for $T_{5/3}$.

Analysis improves previous constraints on these particles.

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.