Measurement of Cabibbo-Suppressed Decays of theτLepton

Branching ratios for the dominant Cabibbo-suppressed decays of the $\tau$ lepton have been measured by CLEO II in $e^{+}{e}^{-}$ annihilation at the Cornell Electron Storage Ring ($\sqrt{s}\sim 10.6$ GeV) using kaons with momenta below 0.7 GeV/c. The inclusive branching ratio into one charged kaon is (1.60 ± 0.12 ± 0.19)%. For the exclusive decays, $B({\tau }^{-}\to K^{-}{\nu }_{\tau })=(0.66\mathrm{}\pm 0.07\pm 0.09)\%$, $B({\tau }^{-}\to K^{-}{\pi }^0{\nu }_{\tau })=(0.51\mathrm{}\pm 0.10\pm 0.07)\%$, and, based on three events, $B({\tau }^{-}\to K^{-}2{\pi }^0{\nu }_{\tau })<\mathrm{}0.3\%$ at the 90% confidence level. These represent significant improvements over previous results. $B({\tau }^{-}\to K^{-}{\pi }^0{\nu }_{\tau })$ is measured for the first time with exclusive ${\pi }^0$ reconstruction.