Fourth-generation quarks and leptons

Abstract

We study the production, decay, and detection of fourth-generation quarks and leptons at present and future hadron colliders. We use a plausible extension of the quark-mixing systematics of three generations. We consider a range of heavy-quark masses that include overlapping generations and superheavy quarks that decay to the $W$ boson. One particularly intriguing possibility is a new charge $-\frac{1}{3}$ quark ($v$) with mass comparable to the $t$-quark mass. Hadronic $v\bar{v}$ production could exceed $t\bar{t}$ production, but there would be no substantial analog to the $W\to t\bar{b}$ source. The $v\to c$ decay would resemble $t\to b$ decay in many respects, except that the $v$ lifetime is long and might be measurable with microvertex detectors. We discuss how the cluster transverse mass, the identification of $b$ and $c$ hadrons, and possible diffractive leading-particle effects might differentiate between $v$ and $t$ semileptonic-decay signals. Electroweak $W^{+}{W}^{-}$ pair production is also evaluated as a benchmark with which superheavy-quark signals can be compared.