Search for the Lepton Flavor Violation Processes $J/\psi \to$ $\mu\tau$ and $e\tau$

TL;DR

This study searches for lepton flavor violation in $J/\psi$ decays to $\mu\tau$ and $e\tau$, setting upper limits on their branching ratios using data from the BESII detector, with no significant signals observed.

Contribution

First search for lepton flavor violation in $J/\psi$ decays to $\mu\tau$ and $e\tau$, establishing new upper limits on their branching ratios.

Findings

No significant lepton flavor violation signals observed.

Upper limits on branching ratios are $2.0 \times 10^{-6}$ for $J/\psi \to \mu\tau$.

Upper limit of $8.3 \times 10^{-6}$ for $J/\psi \to e\tau$.

Abstract

The lepton flavor violation processes $J/\psi \to \mu\tau$ and $e\tau$ are searched for using a sample of 5.8$\times 10^7$ $J/\psi$ events collected with the BESII detector. Zero and one candidate events, consistent with the estimated background, are observed in $J/\psi \to \mu\tau, \tau\to e\bar\nu_e\nu_{\tau}$ and $J/\psi\to e\tau, \tau\to\mu\bar\nu_{\mu}\nu_{\tau}$ decays, respectively. Upper limits on the branching ratios are determined to be $Br(J/\psi\to\mu\tau)<2.0 \times 10^{-6}$ and $Br(J/\psi \to e\tau) < 8.3 \times10^{-6}$ at the 90% confidence level (C.L.).