Measurement of Cabibbo Suppressed Decays of the $τ$ Lepton

Branching ratios for the dominant Cabibbo-suppressed decays of the $\tau$ lepton have been measured by CLEO~II in $e^+ e^-$ annihilation at CESR ($\sqrt{s} \sim 10.6$~GeV) using kaons with momenta below $0.7\ \rm GeV/c$. The inclusive branching ratio into one charged kaon is $(1.60 \pm 0.12 \pm 0.19)\%$. For the exclusive decays, $B(\tau \to K^-) = (0.66 \pm 0.07 \pm 0.09)\%$, $B(\tau \to K^- \pi^0) = (0.51 \pm 0.10 \pm 0.07)\%$, and, based on three events, $B(\tau \to K^- \pi^0 \pi^0) < 0.3\%$ at the 90\% confidence level. These represent significant improvements over previous results. $B(\tau\to K^- \pi^0)$ is measured for the first time with exclusive $\pi^0$ reconstruction.