Improved Determination of the Width of the Top Quark
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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 Β(t → Wb). Γ(t → Wb) is obtained from the t-channel single top-quark production cross section and Β(t → Wb) is measured in tt- events. For a top mass of 172.5 GeV, the resulting width is Γt = 2.00 +0:47 - 0:43 GeV. This translates to a top-quark lifetime of τt = (3.29 +0:90 -0.63) x 10-25s. 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.