Improved determination of the width of the top quark

Abstract

We present an improved determination of the total width of the top quark, Γt, using 5.4 fb−1 of integrated luminosity collected by the D0 Collaboration at the Tevatron pp¯ Collider. The total width Γt is extracted from the partial decay width Γ(t→Wb) and the branching fraction B(t→Wb).Γ(t→Wb) is obtained from the t-channel single top-quark production cross section and B(t→Wb) is measured in tt¯ events. For a top mass of 172.5 GeV, the resulting width is Γt=2.00−0.43+0.47 GeV. This translates to a top-quark lifetime of τt=(3.29−0.63+0.90)×10−25 s. We also extract an improved direct limit on the Cabibbo-Kobayashi-Maskawa quark-mixing matrix element 0.81<|Vtb|≤1 at 95% C.L. and a limit of |Vtb′|<0.59 for a high-mass fourth-generation bottom quark assuming unitarity of the fourth-generation quark-mixing matrix.