We present an improved determination of the total width of the top quark, ${\Gamma }_t$, using $5.4{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the D0 Collaboration at the Tevatron $p\overline{p}$ 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 $t\overline{t}$ events. For a top mass of 172.5 GeV, the resulting width is ${\Gamma }_t={2.00}_{-0.43}^{+0.47}\mathrm{GeV}$. This translates to a top-quark lifetime of ${\tau }_t=({3.29}_{-0.63}^{+0.90})\times {10}^{-25}\mathrm{s}$. We also extract an improved direct limit on the Cabibbo-Kobayashi-Maskawa quark-mixing 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.

• Received 20 January 2012

DOI:https://doi.org/10.1103/PhysRevD.85.091104