Precise measurement of the lifetime of the tau lepton

Data accumulated with a high-precision vertex drift chamber operating in the MAC detector at the SLAC storage ring PEP are used for a precise measurement of the lifetime of the τ lepton. We measure decay lengths of a sample of reconstructed three-prong decay vertices, and impact parameters of a separate sample of decay tracks. Combining these results, we find that ${\tau }_{\tau }$=0.309±0.019 ps, in agreement with the prediction from the measured leptonic branching ratio and τ-μ universality.