Measurement of the tau branching fractions into leptons

Using data collected with the L3 detector near the Z resonance, corresponding to an integrated luminosity of 150 pb-l, the branching fractions of the tau lepton into electron and muon are measured to be beta(tau --> e<()over bar>(e)nu (tau)) = (17.806 +/- 0.104 (stat.) +/- 0.076 (syst.))%, beta(tau --> mu<()over bar>(mu)nu (tau)) = ( 17.342 +/- 0.110 (stat.) +/- 0.067 (syst.))%. From these results the ratio of the charged current coupling constants of the muon and the electron is determined to be g(mu)/g(e) = 1.0007 +/- 0.0051. Assuming electron-muon universality, the Fermi constant is measured in tau lepton decays as G(F) = (1.1616 +/- 0.0058) x 10(-5) GeV-2. Furthermore, the coupling constant of the strong interaction at the tau mass scale is obtained as alpha (s)(m(tau)(2)) = 0.322 +/- 0.009 (exp.) +/- 0.015 (theory), (C) 2001 Elsevier Science B,V. All rights reserved.