Measurement ofτLifetime 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 $\sqrt{s}=29\mathrm{}$ GeV. We find ${\tau }_{\tau }=(3.15\mathrm{}\pm 0.36\pm 0.4)\times {10}^{-13\mathrm{}}$ sec. Results for the topological branching ratios $B_1$, $B_3$, $B_5$ ($\tau$ decaying into 1, 3, 5 charged particles) are $B_3\equiv 1-B_1=0.133\mathrm{}\pm 0.003\pm 0.006$ and $B_5<0.0017\mathrm{}$ at the 95% confidence level. The fraction of all three-prong decays unaccompanied by ${\pi }^0\text{'}\mathrm{s}$ is found to be 0.61±0.03±0.05.