Search for the charged lepton flavor violating decay $\psi(3686)\to e^{\pm}\mu^{\mp}$

TL;DR

This study conducted the first search for the charged lepton flavor violating decay of $ ext{psi}(3686)$ into an electron and a muon, using a large dataset, and set a new upper limit on its branching fraction.

Contribution

It provides the first experimental search for $ ext{psi}(3686) o e^{\pm}\mu^{\mp}$ decay and establishes an upper limit on its branching fraction.

Findings

No signal was observed for the decay.

An upper limit on the branching fraction was set at $1.4 imes 10^{-8}$.

The result constrains new physics models predicting such decay.

Abstract

By analyzing $(2367.0\pm11.1)\times10^6$ $\psi(3686)$ events collected in $e^+e^-$ collisions at $\sqrt{s}=3.686~\rm GeV$ with the BESIII detector at the BEPCII collider, we report the first search for the charged lepton flavor violating decay $\psi(3686)\to e^{\pm}\mu^{\mp}$. No signal is found. An upper limit on the branching fraction $\mathcal{B}(\psi(3686)\to e^{\pm}\mu^{\mp})$ is determined to be $1.4\times10^{-8}$ at the 90\% confidence level.