Rashmi Dhamija

26 February 2024
QWG 2024 - The 16th International Workshop on Heavy Quarkonium

Abstract: We report a search for the charged-lepton flavor violation in $\Upsilon(2S)\to \ell^{\mp}\tau^{\pm} (\ell= e,\mu)$ decays using a 25 $\rm{fb}^{-1} \Upsilon(2S)$ sample collected by the Belle detector at the KEKB $e^{-}e^{+}$ asymmetric-energy collider. We find no evidence for a signal and set upper limits on the branching fractions (B) at a 90% confidence level. We obtain the most stringent upper limits: $\mathcal{B}(\Upsilon(2S) \to \mu^{\mp}\tau^{\pm}) < 0.23 × 10^{-6}$ and $\mathcal{B}(\Upsilon(2S) \to e^{\mp}\tau^{\pm}) < 1.12 × 10^{-6}$.