Determination of the width of the top quark

TL;DR

This paper measures the total decay width of the top quark using data from the D0 experiment at the Tevatron, providing the most precise estimate to date and setting limits on new physics involving a fourth-generation quark.

Contribution

First measurement of the top quark's total width using combined decay and production data, including limits on a hypothetical fourth-generation quark mixing.

Findings

Top quark width: 1.99 +0.69 -0.55 GeV

Top quark lifetime: (3.3 +1.3 -0.9) x 10^-25 s

Upper limit on |Vtb'| < 0.63 at 95% C.L.

Abstract

We extract the total width of the top quark, Gamma_t, from the partial decay width Gamma(t -> W b) measured using the t-channel cross section for single top quark production and from the branching fraction B(t -> W b) measured in ttbar events using up to 2.3 fb^-1 of integrated luminosity collected by the D0 Collaboration at the Tevatron ppbar Collider. The result is Gamma_t = 1.99 +0.69 -0.55 GeV, which translates to a top-quark lifetime of tau_t = (3.3 +1.3 -0.9) x 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 |Vtb'| < 0.63 at 95% C.L.