Measurement of $\mathcal{B}(t\to Wb)/\mathcal{B}(t\to Wq)$ at the Collider Detector at Fermilab

We present a measurement of the ratio of top-quark branching fractions $R=\mathcal{B}(t\to Wb)/\mathcal{B}(t\to Wq)$, where $q$ can be a $b$, $s$, or a $d$ quark, using lepton-plus-jets and dilepton data sets with an integrated luminosity of $\sim 162{\mathrm{pb}}^{-1}$ collected with the Collider Detector at Fermilab during Run II of the Tevatron. The measurement is derived from the relative numbers of $t\overline{t}$ events with different multiplicity of identified secondary vertices. We set a lower limit of $R>0.61$ at 95% confidence level.

Figure 1

Fit of the ANN output in the 0-tag $\mathrm{L}+\mathrm{J}$ data set (triangles) with a sum of 3 components: $W+\mathrm{\text{jets}}$ (upper), QCD multijet (middle), and $t\overline{t}$ (lower). The QCD normalization is independently estimated and not varied in the fit; its shape is determined from the nonisolated lepton data.

Figure 2

The upper plot shows the likelihood as a function of $R$ (inset) and its negative logarithm. The intersections of the horizontal line $\ln (L)=-0.5$ with the likelihood define the statistical $1\sigma$ errors on $R$. The lower plot shows 95% (outer), 90% (central), and 68% (inner) C.L. bands for $R_{\mathrm{true}}$ as a function of $R$. Our measurement of $R=1.12$ (vertical line) implies $R>0.61$ at the 95% C.L. (horizontal line).