Search for the rare semi-leptonic decay J/ψ → D − e+ ν e + c.c.

Using 10.1 × 109 J/ψ events produced by the Beijing Electron Positron Collider (BEPCII) at a center-of-mass energy $\sqrt{s}$ = 3.097 GeV and collected with the BESIII detector, we present a search for the rare semi-leptonic decay J/ψ → D − e + ν e + c.c. No excess of signal above background is observed, and an upper limit on the branching fraction ℬ(J/ψ → D − e + ν e + c. c.) < 7.1 × 10−8 is obtained at 90% confidence level. This is an improvement of more than two orders of magnitude over the previous best limit.