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/sup -1/ the lifetime of the tau lepton is measured to be tau /sub tau /=293.2+or-2.0 (stat.)+or-1.5(sys.) fs, and the branching ratios of the tau lepton into electron and muon are measured to be B( tau to e nu /sub e/ nu /sub tau /)=(17.806+or-0.104 (stat.)+or-0.076(sys.))% and B( tau to mu nu /sub mu / nu /sub tau /)=(17.342+or-0.110 (stat.) +or-0.067(sys.))%, respectively. From these results the ratio of the charged current coupling constants g/sub mu //g/sub e/, g/sub tau //g /sub e/ and g/sub tau //g/sub mu / are determined and support the lepton universality hypothesis. The Fermi-constant and the coupling constant of the strong interaction at the tan mass are obtained from these measurements. (12 refs).