Search for the reactions e+e- -> mu+ tau- and e+e- -> e+ tau-

Abstract

We report on a search for the lepton-flavor-violating processes $e^+e^- \to \mu^+\tau^-$ and $e^+e^- \to e^+\tau^-$. The data sample corresponds to an integrated luminosity of 211 fb$^{-1}$ recorded by the BaBar experiment at the SLAC PEP-II asymmetric-energy B Factory at a center-of-mass energy of $\sqrt{s} = 10.58\ensuremath{\mathrm{Ge\kern -0.1em V}}$. We find no evidence for a signal and set the 90% confidence level upper limits on the cross sections to be $\sigma_{\mu\tau} <3.8$ \ensuremath{fb} and $\sigma_{e\tau} <9.2$\ensuremath{fb}. The ratio of the cross sections with respect to the dimuon cross section are measured to be $\sigma_{\mu\tau}/\sigma_{\mu\mu} < 3.4\times10^{-6}$ and $\sigma_{e\tau}/\sigma_{\mu\mu} < 8.2\times10^{-6}$.