An OPAL measurement of the $\tau^{-} \to e^{-}\nu_{e}\nu_{\tau}$ branching ratio

The branching ratio for the decay tau /sup -/ to e/sup -/ nu /sub e/ nu /sub tau / has been measured using data collected by the OPAL experiment at LEP. In total 33073 tau /sup -/ to e/sup -/ nu /sub e/ nu /sub tau / candidates were identified from a sample of 186197 selected tau decays, giving a branching ratio of B/sub e/= (17.81+or-0.09 (stat)+or-0.06 (syst))This result is combined with other electroweak measurements to test e- mu and mu - tau universality in charged-current weak interactions at the level of 0.5Additionally, a value of the strong coupling constant alpha /sub s/(m/sub tau //sup 2/) has been extracted from B/sub e/ and evolved to the Z/sup 0/ mass scale to give alpha /sub s/(m/sub Z//sup 2/)=0.1204+or-0.0011 (exp)/sub -0.0019//sup +0.0021/ (theory). (16 refs).