Determination of the Width of the Top Quark

We extract the total width of the top quark, ${\Gamma }_t$, from the partial decay width $\Gamma (t\to Wb)$ measured using the $t$-channel cross section for single top-quark production and from the branching fraction $\mathcal{B}(t\to Wb)$ measured in $t\overline{t}$ events using up to $2.3{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the D0 Collaboration at the Tevatron $p\overline{p}$ Collider. The result is ${\Gamma }_t={1.99}_{-0.55}^{+0.69}\mathrm{GeV}$, which translates to a top-quark lifetime of ${\tau }_t=({3.3}_{-0.9}^{+1.3})\times {10}^{-25}\mathrm{s}$. Assuming a high mass fourth generation $b^{\prime }$ quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on $|V_{t{b}^{\prime }}|<0.63$ at 95% C.L.

Figure 1

Representative diagram for $t$-channel single top-quark production.

Figure 2

Probability density for the expected and measured partial width $\Gamma (t\to Wb)$. The hatched areas represent 1 standard deviation around the most probable value.

Figure 3

Probability density for the expected and measured total width ${\Gamma }_t$. The hatched areas represent 1 standard deviation around the most probable value.