First Observation of Electroweak Single Top Quark Production

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