Perturbative QCD corrections to the ratioRforτdecay

Abstract

The perturbative QCD correction to the semihadronic decay rate of a heavy lepton is expressed as an expansion in ${\alpha }_s$. In the case of the τ lepton, the ratio of the semihadronic and electronic decay rates is R=3[1+${\alpha }_s$/π+5.20(${\alpha }_s$/π${)}^2$ +104.0(${\alpha }_s$/π${)}^3$]. The use of R to give a precise determination of ${\alpha }_s$ is advocated.