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

We have measured the ratio R = Gamma(K-L --> gammagamma)/Gamma(K-L --> pi(0)pi(0)pi(0)) using the KLOE detector. From a sample of similar to10(9) phi-mesons produced at DAPhiNE, the Frascati phi-factory, we select similar to1.6 x 10(8) K-L-mesons tagged by observing K-S --> pi(+)pi(-) following the reaction e(+)e(-) --> phi --> KLKS. From this sample we select 27,375 K-L --> gammagamma events and obtain R = (2.79 +/- 0.02(stat) +/- 0.02(syst)) X 10(-3). Using the world average value for BR(K-L --> pi(0)pi(0)pi(0)), we obtain BR(K-L --> gammagamma) = (5.89 +/- 0.07 +/- 0.08) x 10(-4) where the second error is due to the uncertainty on the pi(0)pi(0)pi(0) branching fraction. (C) 2003 Published by Elsevier B.V.