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 $e^+e^- \to μ^+τ^-$ and $e^+e^- \to e^+τ^-$. 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 $σ_{μτ} <3.8$ \ensuremath{fb} and $σ_{eτ} <9.2$\ensuremath{fb}. The ratio of the cross sections with respect to the dimuon cross section are measured to be $σ_{μτ}/σ_{μμ} < 3.4\times10^{-6}$ and $σ_{eτ}/σ_{μμ} < 8.2\times10^{-6}$.