Measurement ofτbranching ratios

We have measured the branching ratios for several τ decay modes. We use $e^{+}$ $e^{\mathrm{-}}$→${\tau }^{+}$ ${\tau }^{\mathrm{-}}$ events accumulated with the TPC/Two-Gamma facility at the SLAC $e^{+}$ $e^{\mathrm{-}}$ storage ring PEP. The data correspond to an integrated luminosity of 77 ${\mathrm{pb}}^{\mathrm{-}1}$ at a center-of-mass energy of 29 GeV. The one- and three-charged-particle inclusive branching ratios of the τ decay are measured to be $B_1$=(84.7±1.0)% and $B_3$=(15.1±1.0)%, where $B_1$+$B_3$ is constrained to be 99.85%. The branching ratios of the two leptonic decay modes are B(${\tau }^{\mathrm{-}}$→$e^{\mathrm{-}}$ ν${¯}_e$ ${\nu }_{\tau }$)=(18.4±1.6)% and B(${\tau }^{\mathrm{-}}$→${\mu }^{\mathrm{-}}$ ν${¯}_{\mu }$ ${\nu }_{\tau }$)=(17.7±1.4)%. If we then assume lepton universality, we obtain B(${\tau }^{\mathrm{-}}$→$e^{\mathrm{-}}$ ν${¯}_e$ ${\nu }_{\tau }$)=(18.3±0.9)% and B(${\tau }^{\mathrm{-}}$→${\mu }^{\mathrm{-}}$ ν${¯}_{\mu }$ ${\nu }_{\tau }$)=(17.8±0.9)%. We measure the Cabibbo-allowed semihadronic decay mode B(${\tau }^{\mathrm{-}}$→${\pi }^{\mathrm{-}}$+neutral particles)=(47.0±1.5)%, and the Cabibbo-suppressed τ decay mode B(${\tau }^{\mathrm{-}}$→$K^{\mathrm{-}}$+neutral particles)=(1.6±0.4)%. By looking for associated photons, we find B(${\tau }^{\mathrm{-}}$→$K^{\mathrm{-}}$ ${\pi }^0$+neutral particles) to be (1.2±0.6)%. Using the channel K${\mathrm{*}}^{\mathrm{-}}$→${\mathit{K}}_{\mathit{S}}^{\mathit{O}}$ ${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{\mathrm{-}}$, we find B(${\tau }^{\mathrm{-}}$→$K^{\mathrm{*}\mathrm{-}}$(892)+neutral particles)=(1.4±0.9)%. The quoted errors are the combined statistical and systematic errors.