Single-top-quark production at hadron colliders

Single-top-quark production probes the charged-current weak interaction of the top quark, and provides a direct measurement of the CKM matrix element Vtb. We perform two independent analyses to quantify the accuracy with which the W -gluon fusion (gq → tb̄q) and qq̄ → tb̄ signals can be extracted from the backgrounds at both the Tevatron and the LHC. Although perturbation theory breaks down at low transverse momentum for the W -gluon fusion b̄ differential cross section, we show how to obtain a reliable cross section integrated over low b̄ transverse momenta up to a cutoff. We estimate the accuracy with which Vtb can be measured in both analyses, including theoretical and statistical uncertainties. We also show that the polarization of the top quark in W -gluon fusion can be detected at the Tevatron and the LHC.