Measurement of the branching ratio KL0→2π0 to KL0→3π0

The branching ratio of 2π0 to 3π0 decays of the long-lived neutral kaon has been determined. The number of 2π0 events was taken over from the previous analysis of the CERN-RHEL-Aachen group. A sample of 3π0 decays was collected using events with six visible showers only. The background in the sample was shown to be negligible; the main uncertainty arises from the recognition of 6-shower events. Allowing for this uncertainty, and for systematic effects in extracting the 2π0 signal, the branching ratio found is (0.90±0.30)·10−2. This corresponds to a value of theCP-violating parameter |η00|=(3.2±0.5)·10−3.