Single top quarks at the Tevatron are produced via the electroweak interaction from the decay of an off-shell W boson in the s-channel, or fusion of a virtual W boson with a b quark in the t-channel. In particular, the s-channel production rate is comparatively low at the LHC, and the much larger background contamination at the LHC would make it very difficult to measure the s-channel cross section.
In this talk, I will present the analysis that led to the first evidence for s-channel single top-quark production. The measurement is based on 9.7 fb-1of ppbar collisions at sqrt{s} = 1.96 TeV collected with the D0 detector. Both the s and t-channel cross-sections are simultaneously measured without assuming the standard model prediction for either, and the CKM quark mixing element |Vtb|, which describes the Wtb coupling, is directly determined.
