The Top Width - Theoretical update

TL;DR

This paper provides a precise Standard Model prediction for the top-quark width by combining QCD corrections with finite $b$-mass and $W$ width effects, along with complete one-loop electroweak corrections. It uses the JK1 framework for the QCD decay rate and DS results for electroweak corrections, and it analyzes various approximations (narrow width, massless $b$) against a realistic input set. A key result is that the $W$ width effect is comparable in size to the electroweak corrections, and both are at the percent level, constrained by uncertainties in $\alpha_s$ and $m_t$. The work highlights the threshold region in $e^+e^-$ to $t\bar t$ as the most favorable for precision measurements and provides a practical, ~1% accurate prediction for $\Gamma_t$.

Abstract

A critical assessment of the available calculations of the top quark width is presented. QCD corrections, the finite mass of the $b$ quark and the effect of the $W$ width are included as well as the electroweak corrections. The relative importance of these corrections is demonstrated for the realistic range of top masses. For the QCD corrected decay rate we use the formulae from \cite{JK1} and include the electroweak correction taken from \cite{DS}. Our results differ from those available in the literature because all the later calculations ignored the effect of W width discussed earlier in \cite{JK1}~. This leads to an effect comparable in size to the electroweak correction.