Measurement of the Branching Fraction for the Cabibbo-Suppressed Decayτ−→K−ντ

The branching fraction for the Cabibbo-suppressed decay ${\tau }^{-}\to K^{-}{\nu }_{\tau }$ is measured from data obtained with the Mark II detector at SPEAR. Fifteen events containing a $K^{\pm }$ in coincidence with a muon or electron of opposite charge are observed. It is determined that $B({\tau }^{-}\to K^{-}{\nu }_{\tau })=(1.3\mathrm{}\pm 0.5)\%$.