A search for the lepton flavour violating decays $\tau^- \to l^- K^0_{ \scriptscriptstyle S}$ ($l = e$ or $\mu$) has been performed using a data sample corresponding to an integrated luminosity of 469 ${ fb}^{ -1}$, collected with the { \slshape B\kern-0.1em{ \smaller A}\kern-0.1em B\kern-0.1em{ \smaller A\kern-0.2em R}} detector at the SLAC PEP-II $e^+e^-$ asymmetric energy collider. No statistically significant signal has been observed in either channel and the estimated upper limits on branching fractions are ${ \cal B}(\tau^- \to e^- K^0_{ \scriptscriptstyle S}) < 3.3 \times 10^{ -8}$ and ${ \cal B}(\tau^- \to \mu^- K^0_{ \scriptscriptstyle S}) < 4.0 \times 10^{ -8}$ at 90% confidence level.
Categories: hep-ex