Measurement of R = \boldmath${\mathcal{B}(t \rightarrow Wb)/\mathcal{B}(t \rightarrow Wq)} $ in Top--quark--pair Decays using Lepton+jets Events and the Full CDF Run II Data set

Abstract

We present a measurement of the ratio of the top-quark branching fractions $R=\mathcal{B}(t\rightarrow Wb)/\mathcal{B}(t\rightarrow Wq)$, where $q$ represents quarks of type $b$, $s$, or $d$, in the final state with a lepton and hadronic jets. The measurement uses $\sqrt{s}$ = 1.96 TeV proton--antiproton collision data from 8.7 fb$^{-1}$ of integrated luminosity collected with the Collider Detector at Fermilab during Run II of the Tevatron. We simultaneously measure $R=0.94 \pm 0.09$ (stat+syst), the $t\bar{t}$ production cross section $\sigma_{t \bar t} = 7.5 \pm 1.0$ (stat+syst) pb. The magnitude of the Cabibbo-Kobayashi-Maskawa matrix element, $|V_{tb}| = 0.97 \pm 0.05$ (stat+syst) is extracted assuming three generations of quarks, and a lower limit of $|V_{tb}|>0.89$ at 95% credibility level is set.