Observation of Electroweak Single Top-Quark Production

We report the observation of single top-quark production using $3.2{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collision data with $\sqrt{s}=1.96\mathrm{TeV}$ collected by the Collider Detector at Fermilab. The significance of the observed data is 5.0 standard deviations, and the expected sensitivity for standard model production and decay is in excess of 5.9 standard deviations. Assuming $m_t=175\mathrm{GeV}/c^2$, we measure a cross section of ${2.3}_{-0.5}^{+0.6}(\mathrm{stat}+\mathrm{syst})\mathrm{pb}$, extract the CKM matrix-element value $|V_{tb}|=0.91\pm 0.11(\mathrm{stat}+\mathrm{syst})\pm 0.07(\mathrm{\text{theory}})$, and set the limit $|V_{tb}|>0.71$ at the 95% C.L.

Figure 1

Discriminant distributions for the $\ell +{\mathrm{E̸}}_T+\mathrm{\text{jets}}$ analyses. The data are indicated with points, and the predictions are shown separately for each contribution with stacked histograms. The signal expectations shown are the SM predictions. The insets show the distributions of the candidate events in the high-discriminant region.

Figure 2

Discriminant distributions for the (a) SD, and (b) MJ analyses (see Fig. 1 for their caption and legend). (c) shows the distribution of the likelihood ratio test statistic $-2\ln Q$.