Search for the lepton flavor violating decay J/ψ → eμ

Abstract

We present a search for the lepton flavor violating decay J/ψ → e±μ∓ using 8.998 × 109J/ψ events collected with the BESIII detector at the BEPCII e+e− storage ring. No excess of signal above background is observed; we therefore set an upper limit on the branching fraction of ℬ(J/ψ→e±μ∓)<4.5×10−9 at the 90% confidence level. Improving the previous best result by a factor of more than 30, this measurement places the most stringent limit to date on lepton flavor violation in the heavy quarkonium sector.