Observation of Single Top Quark Production and Measurement of |Vtb| with CDF

TL;DR

This paper reports the first observation of single top quark production at Fermilab, measuring the production cross section and the CKM matrix element |Vtb| with high statistical significance, confirming the standard model predictions.

Contribution

It presents the first observation of electroweak single top quark production and provides precise measurements of the cross section and |Vtb|, using advanced multivariate analysis techniques.

Findings

Observation of single top quark production with 5.0 sigma significance

Measured cross section of 2.3+0.6-0.5 pb

Determined |Vtb|=0.91+0.11-0.11 and set a lower limit >0.71

Abstract

We report the observation of electroweak single top quark production in 3.2 fb-1 of ppbar collision data collected by the Collider Detector at Fermilab at sqrt{s}=1.96 TeV. Candidate events in the W+jets topology with a leptonically decaying W boson are classified as signal-like by four parallel analyses based on likelihood functions, matrix elements, neural networks, and boosted decision trees. These results are combined using a super discriminant analysis based on genetically evolved neural networks in order to improve the sensitivity. This combined result is further combined with that of a search for a single top quark signal in an orthogonal sample of events with missing transverse energy plus jets and no charged lepton. We observe a signal consistent with the standard model prediction but inconsistent with the background-only model by 5.0 standard deviations, with a median expected sensitivity in excess of 5.9 standard deviations. We measure a production cross section of 2.3+0.6-0.5(stat+sys) pb, extract the CKM matrix element value |Vtb|=0.91+0.11-0.11 (stat+sys)+-0.07(theory), and set a lower limit |Vtb|>0.71 at the 95% confidence level, assuming m_t=175 GeVc^2.