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.