Search for the lepton number violating process J/ψ→K⁺K⁺e⁻e⁻+c.c.

Based on (10087 ± 44) × 10⁶ J/ψ events collected with the BESIII detector, we search for the lepton number violating decay J/ψ → K⁺K⁺e⁻e⁻ + c.c. for the first time. The upper limit on the branching fraction of this decay is set to 2.1 × 10⁻⁹ at the 90% confidence level with a frequentist method. This is the first search for J/ψ decays with a lepton number change by two, offering valuable insights into the underlying physical processes.