Determination of the width of the top quark

Abstract

We extract the total width of the top quark, Γ_t, from the partial decay width Γ(t→ Wb) measured using the t-channel cross section for single top-quark production and from the branching fraction B(t→ Wb) measured in tt‾ events using up to 2.3 fb^-1 of integrated luminosity collected by the D0 Collaboration at the Tevatron pp‾ Collider. The result is G_t=1.99_-0.55^+0.69 GeV, which translates to a top-quark lifetime of t_t=(3.3_-0.9^+1.3)×10^-25 s. Assuming a high mass fourth generation b' quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on |V_tb'|<0.63 at 95% C.L.