Observation of Electroweak Single Top-Quark Production

We report the observation of single top-quarkproduction using 3.2 fb{sup -1} of pp collision data with sq root(s)=1.96 TeV collected by the Collider Detectorat 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{sub t}=175 GeV/c{sup 2}, we measure a cross section of 2.3{sub -0.5}{sup +0.6}( stat+syst) pb, extract the CKM matrix-element value |V{sub tb}|=0.91+-0.11( stat+syst)+-0.07(theory), and set the limit |V{sub tb}|>0.71 at the 95% C.L.