Search for charged lepton flavor violation in $J/\psi$ decays at BESIII

TL;DR

This study searches for charged lepton flavor violation in $J/$ decays at BESIII, setting the most stringent upper limits to date, which constrains new physics models beyond the Standard Model.

Contribution

First search for CLFV in $J/\psi$ decays at BESIII, significantly improving experimental limits and providing new constraints on theories beyond the Standard Model.

Findings

Upper limit for $J/\psi\to e\tau$ decay is $7.5\times 10^{-8}$

Upper limit for $J/\psi\to e\mu$ decay is $4.5\times 10^{-9}$

Results are the most stringent CLFV limits in heavy quarkonium systems.

Abstract

In the Standard Model, charged lepton flavor violation (CLFV) is heavily suppressed by tiny neutrino mass, while many theoretical models can enhance CLFV effects up to a detectable level. The observation of any CLFV process would be a clear signal of new physics beyond SM. BESIII experiment collected 10 billion $J/\psi$ data and searched for CLFV processes $J/\psi\to e\tau$ and $e\mu$. The upper limits at the 90% confidence level are determined to be $\mathcal{B}(J/\psi\to e\tau)<7.5\times 10^{-8}$ and $\mathcal{B}(J/\psi\to e\mu)<4.5\times 10^{-9}$, respectively. Improving the previously experimental limits by two orders of magnitudes, the results are the most stringent CLFV searches in the heavy quarkonium system.