Search for Lepton Flavor Violation in $\Upsilon (1S)$ Decays
Résumé
We present a search for charged lepton flavor violation in $\Upsilon (1S)\rightarrow \ell \ell ^\prime [\ell ,\ell ^\prime =e,\mu ,\tau ]$ decays using the 25 $\textrm{fb}^{-1}\Upsilon (2S)$ collected by the Belle detector. Using the Monte Carlo background, we estimate the upper limits of the branching fractions at 90% confidence level.