Measurement of tau lifetime and branching ratios.

Precise results are reported for the tau-lepton lifetime and several tau branching ratios obtained with the MAC detector operating at PEP at ..sqrt..s = 29 GeV. We find tau/sub tau/ = (3.15 +- 0.36 +- 0.4) x 10 /sup -13/ sec. Results for the topological branching ratios B/sub 1/, B/sub 3/, B/sub 5/ (tau decaying into 1, 3, 5 charged particles) are B/sub 3/equivalent1-B/sub 1/ = 0.133 +- 0.003 +- 0 .006 and B/sub 5/<0.0017 at the 95% confidence level. The fraction of all three-prong decays unaccompanied by ..pi../sup 0/'s is found to be 0.61 +- 0.03 +- 0.05.