Measurement of \boldmath $R=\mathcal{B}\left(t\to Wb\right)/\mathcal{B}\left(t\to Wq\right)$ in Top--Quark--Pair Decays using Dilepton Events and the Full CDF Run II Data Set

Abstract

We present a measurement of the ratio of the top-quark branching fractions $R=\mathcal{B}(t\to Wb)/\mathcal{B}(t\to$ $q$ represents quarks of flavors $b$, $s$, or $d$, in the final state, in events with two charged leptons, missing transverse energy and at least two jets. The measurement uses $\sqrt{s}$ = 1.96 TeV proton--antiproton collision data corresponding to an integrated luminosity of 8.7 fb${}^{-1}$ and collected with the Collider Detector at Fermilab during Run II of the Tevatron. We measure $R=0.87\pm 0.07$ (stat+syst), and extract the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element, $\left|V_{tb}\right|=0.93\pm 0.04$ (stat+syst) assuming three generations of quarks. Under these assumptions, a lower limit of $|V_{tb}|>0.85$ at 95% credibility level is set.

submitted to PRL