Measurement of the tau lifetime and leptonic branching ratios in L3

Using data collected with the L3 detector near the Z resonance corresponding to an integrated luminosity of 150 pb(-1) the lifetime of the tau lepton is measured to be tau (T) = 293.2 +/- 2.0(stat.) +/- 1.5(sys.) fs, and the branching ratios of the tau lepton into electron and muon are measured to be beta(tau --> e (v) over bar (e)v tau) = (17.806 +/- 0.104 (stat.)+/-0.076(sys.))% and beta(tau --> mu(v) over bar (mu)v tau) = (17.342 +/- 0.110 (stat.) +/-0.067(sys.))%, respectively. From these results the ratio of the charged current coupling constants g(mu)/g(e), g(tau)/g(e) and g(r)/g(mu) are determined and support the lepton universality hypothesis. The Fermi-constant and the coupling constant of the strong interaction at the tau mass are obtained from these measurements.