Search for the charged lepton flavor violating decay $J/\psi\to e\tau$

TL;DR

This study searches for a rare lepton flavor violating decay of the $J/\psi$ particle into an electron and tau, finding no signal but setting a much stricter upper limit on its occurrence.

Contribution

The paper provides the first search for $J/\psi \to e\tau$ decay with a significantly improved upper limit, enhancing constraints on new physics models.

Findings

No significant $J/\psi \to e\tau$ signal observed.

Upper limit on branching fraction set at $7.5 \times 10^{-8}$.

Limit improved by two orders of magnitude.

Abstract

A search for the charged lepton flavor violating decay $J/\psi\to e^{\pm}\tau^{\mp}$ with $\tau^{\mp} \to \pi^{\mp}\pi^0\nu_{\tau}$ is performed with about $10$ billion $J/ \psi$ events collected with the BESIII detector at the BEPCII. No significant signal is observed, and an upper limit is set on the branching fraction $\mathcal{B}(J/\psi\to e^{\pm}\tau^{\mp})<7.5\times10^{-8}$ at the 90$\%$ confidence level. This improves the previously published limit by two orders of magnitude.