Estimation of the branching ratio of the decay KL0-->e+e-e+e- from the KL0-->e+e-X process.

In an experiment to search for the decay K L 0 →ee using the 12-GeV Proton Synchrotron at KEK, we observed 18 events with the e + e − effective mass greater than 470 MeV/c 2 . They are presumed to come mainly from the decay K L 0 → e + e − e + e − . Subtracting the background from the decay K L 0 →eeγ and the external conversion of γ in the decays K L 0 → γγ and K L 0 → eeγ, the branching ratio of the decay K L 0 →e + e − e + e − is estimated to be (6±2±1)×1O −8 . It is consistent with the previous experimental values