Three different techniques are used to measure the mean decay length of the tau lepton with a high precision vertex detector in a sample of 11 800 tau pairs coming from Z decays, collected in 1991 by ALEPH at LEP. Events in which both tau's decay into one charged track are analyzed using two largely independent methods. Displaced vertices in three-prong decays yield another independent measurement. The derived lifetime is 295.5 +/- 5.9 +/- 3.1 fs, using m(tau) = 1777.1 +/- 0.5 MeV/c2. Including previous (1989-1990) ALEPH measurements, the combined tau lifetime is 294.7 +/- 5.4 +/- 3.0 fs.
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