Determination of the τ lifetime

The mean lifetime of the τ lepton is measured from a sample of Z→τ+τ- decays observed with the ALEPH detector at LEP in 1991. Three different techniques are used to extract the lifetime. Two of them are applied to the events containing two one-prong decays, and measure the lifetime from the observed correlation between the sum or the difference of impact parameters and azimuthal angles of the two charged tracks. The lifetime is also determined from measured vertex displacements for three-prong decays. The combined result for the 1991 data sample is ττ=296±5(stat)±4(syst) fs. Together with an earlier ALEPH measurement a lifetime of ττ=295±6 fs is obtained. (author) 9 refs.; 1 fig