Measurement of the ratio Γ(KL→γγ)/Γ(KL→π0π0π0) with the KLOE detector

Abstract We have measured the ratio R = Γ ( K L → γγ )/ Γ ( K L → π 0 π 0 π 0 ) using the KLOE detector. From a sample of ∼10 9 φ -mesons produced at DAΦNE, the Frascati φ -factory, we select ∼1.6×10 8 K L -mesons tagged by observing K S → π + π − following the reaction e + e − → φ → K L K S . From this sample we select 27,375 K L → γγ events and obtain R =(2.79±0.02 stat ±0.02 syst )×10 −3 . Using the world average value for BR( K L → π 0 π 0 π 0 ), we obtain BR( K L → γγ )=(5.89±0.07±0.08)×10 −4 where the second error is due to the uncertainty on the π 0 π 0 π 0 branching fraction.