Precise measurements of the KS->gamma gamma and KL->gamma gamma decay rates

The KS->gamma gamma decay rate has been measured with the NA48 detector using a high intensity short neutral beam from the CERN SPS. The measured branching ratio BR(KS->gamma gamma)=(2.78+-0.06(stat)+-0.04(syst))x10-6, obtained from 7461+-172 KS->gamma gamma events, is significantly higher than the O(p^4) prediction of Chiral Perturbation Theory. Using a KL beam the ratio BR(KL->gamma gamma)/BR(KL->3pi0)=(2.81+-0.01(stat)+-0.02(syst))x10-3 has been measured.