Search for the weak decays J/ψ → D^(∗)- _s e⁺ν_e + c.c

Using a sample of 2.25 × 10⁸ J/ψ events collected with the BESIII detector at the BEPCII collider, we search for the J/ψ semileptonic weak decay J/ψ → D^- _s e⁺ν_e+ c.c. with a much higher sensitivity than previous searches. We also perform the first search for J/ψ → D^∗- _s e⁺ν_e + c.c. No significant excess of a signal above background is observed in either channel. At the 90% confidence level, the upper limits are determined to be B(J/ψ → D^- _s e⁺ν_e + c.c. )< 1.3 × 10^-6 and B(J=ψ → D^∗- _s e⁺ν_e + c.c. ) < 1.8 × 10^-6, respectively. Both are consistent with Standard Model predictions.