Precise measurement of the lifetime of the tau lepton.

Abstract

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 \ensuremath{\tau} 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 ${\ensuremath{\tau}}_{\ensuremath{\tau}}$=0.309\ifmmode\pm\else\textpm\fi{}0.019 ps, in agreement with the prediction from the measured leptonic branching ratio and \ensuremath{\tau}-\ensuremath{\mu} universality.