Search for the Lepton Flavor Violation Process $J/\psi \to e\mu$ at BESIII

TL;DR

This study searches for the rare lepton-flavor-violating decay of J/psi into an electron and a muon, setting an upper limit on its branching fraction using data from the BESIII detector.

Contribution

First search for the decay J/psi to e mu at BESIII, establishing an upper limit on its branching fraction and providing constraints on new physics models.

Findings

No significant signal observed.

Upper limit on branching fraction: < 1.5 x 10^{-7}.

Consistent with background expectations.

Abstract

We search for the lepton-flavor-violating decay of the $J/\psi$ into an electron and a muon using $(225.3\pm2.8)\times 10^{6}$ $J/\psi$ events collected with the BESIII detector at the BEPCII collider. Four candidate events are found in the signal region, consistent with background expectations. An upper limit on the branching fraction of $\mathcal{B}(J/\psi \to e\mu)< 1.5 \times 10^{-7}$ (90% C.L.) is obtained.