Observation of the decay KL0→π±π0e∓ν

Abstract The rare decay KL0→π±π0e∓ν has been observed in an experiment using a MWPC spectrometer and a lead glass counter hodoscope. The observed branching ratio Γ(KL0→π±π0e∓ν)Γ(KL0→all)=(6.2±2.0) × 10−5 agrees well with the theoretical prediction. The charged pion angular distribution was found to be consistent with l = 1 as expected from the |ΔI|=½ rule.