L3 measurement of the tau lepton lifetime

The tau lepton lifetime is measured with the L3 detector at LEP. For the an alysis presented here tau pairs produced during 1994 and 1995 around the Z pole are used. The measurement is done by a decay length method for the 3-p rong tau decays and by an impact parameter analysis for the 1-prong decays. From the data 6 620 3-prong decays are selected, from which a lifetime of tau(tau) = 291.4 +/- 3.9 (stat) +/- 2.0 (syst) fs is determined. The impact parameter analysis on 58 656 1-prong decays results in a lifetime of tau(t au) = 290.5 +/- 2.7 (stat) +/- 2.9 (syst) fs. Combination with our previous results gives tau(tau) = 291.7 +/- 2.0 (stat) +/- 1.8 (syst) fs. These num bers are preliminary.