Observation of electromagnetic Dalitz decays J/ψ → Pe⁺e^-

Based on a sample of (225.3 ± 2.8) × 10⁶ J/ψ events collected with the BESIII detector, the electromagnetic Dalitz decays of J/ψ → Pe⁺e^- (P = η'/η/π^∗0) are studied. By reconstructing the pseudoscalar mesons in various decay modes, the decays J/ψ → η' e⁺e^-, J/ψ → η e⁺e^-, and J/ψ → π⁰ e⁺e^- are observed for the first time. The branching fractions are determined to be B(J/ψ → η' e⁺e^-) = (5.81 ± 0.16 ± 0.31) × 10^-5, B(J/ψ → η e⁺e^-) = (1.16 ± 0.07 ± 0.06) × 10^-5, and B(J/ψ → π⁰ e⁺e^-) = (7.56 ± 1.32 ±0.50) × 10^-7, where the first errors are statistical and the second ones systematic.