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

We present a search for the lepton flavor violating decay J/psi -> e(+/-)mu(-/+) using 8.998 x 10(9)J/psi 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/psi -> e(+/-)mu(-/+)) < 4.5 x 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.

Automated summary

We performed a search for lepton flavor violating decay J/psi -> e(+/-)mu(-/+) using data collected by the BESIII detector at the BEPCII e(+)e(-) storage ring. No significant signal above background was found, leading to an upper limit on the branching fraction of B(J/psi -> e(+/-)mu(-/+)) < 4.5 x 10(-9) at 90% confidence level. This measurement sets the most stringent limit on lepton flavor violation in the heavy quarkonium sector, improving the previous best result by a factor of more than 30.