Search for Lepton Flavour Violating Decays $\tau \to \ell K_S^0$ with the BaBar Experiment

Abstract

A search for the lepton flavour violating decays ${\tau }^{-}\to l^{-}{K}_S^0$ ($l=e$ 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 $\mathcal{B}({\tau }^{-}\to e^{-}{K}_S^0)<3.3\times 10^{-8}$ and $\mathcal{B}({\tau }^{-}\to {\mu }^{-}{K}_S^0)<4.0\times 10^{-8}$ at 90% confidence level.

9 pages, 8 postscript figures, submitted to Phys. Rev. D