An improved determination of the width of the top quark

Abstract

We present an improved determination of the total width of the top quark, ${\Gamma }_t$, using 5.4 fb${}^{-1}$ of integrated luminosity collected by the D0 Collaboration at the Tevatron $p\bar{p}$ Collider. The total width ${\Gamma }_t$ is extracted from the partial decay width $\Gamma (t\to Wb)$ and the branching fraction $\mathcal{B}(t\to Wb)$. $\Gamma (t\to Wb)$ is obtained from the $t$-channel single top quark production cross section and $\mathcal{B}(t\to Wb)$ is measured in $t\bar{t}$ events. For a top mass of $172.5\mathrm{GeV}$, the resulting width is ${\Gamma }_t=2.00_{-0.43}^{+0.47}$ GeV. This translates to a top-quark lifetime of ${\tau }_t=(3.29_{-0.63}^{+0.90})\times 10^{-25}$ s. We also extract an improved direct limit on the CKM matrix element $0.81<|V_{tb}|\le 1$ at 95% C.L. and a limit of $|V_{t{b}^{\prime }}|<0.59$ for a high mass fourth generation bottom quark assuming unitarity of the fourth generation quark mixing matrix.

8 pages, 4 figures, submitted to Phys. Rev. D (RC)