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

TL;DR

This study searches for lepton-flavor-violating processes in electron-positron collisions, finding no evidence and setting upper limits on the cross sections for these rare events.

Contribution

The paper provides the first experimental upper limits on the cross sections for $e^+e^- o au ext{ lepton}$ processes at a specific energy, constraining new physics models.

Findings

No evidence for lepton-flavor violation was observed.

Upper limits on cross sections were set at 3.8 fb and 9.2 fb.

Cross section ratios relative to dimuon production were established.

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 $\sigma_{e\tau}/\sigma_{\mu\mu} < 8.2\times10^{-6}$.