First observation of single-top-quark production

This paper reports the first observation of the electroweak production of single top quarks in p p collisions at a center-of-mass energy of 1.96 TeV based on 2.3 f b-1 and 3.2 f b-1 of data collected by the DZero and Cdf detectors, respectively, at the Fermilab Tevatron Collider. Using various multivariate techniques to separate the small signal from the large background, both experiments obtained a significance of the observed data of 5.0 standard deviations. DZero measures σ(p p → t b + X, t qb + X) 3.94 ± 0.88 p b and Cdf measures 2.3+0.6-0.5 p b. The CKM matrix element that couples the top and the bottom quarks is also measured. DZero reports [Vtb] > 0.78 at 95% C L when f1L =1 and [Vtbf1L] = 1.02 ± 0.12. Cdf measures [Vtb] = 0.91±0.11 (stat + syst)±0.07(theory) and sets the limit [Vtb] > 0.71 at 95% C L.