ChPT test at NA48 and NA62 experiment at CERN

The new published measurements of the K±→π±γγ decay with minimum bias data samples collected by the two experiments NA48/2 and NA62 are discussed. The results include a model independent decay rate measurement and fits to Chiral Perturbation Theory (ChPT) description. The model independent branching ratio in the kinematic range z=(mγγ/mK)2>0.2, obtained by combining the NA48/2 and NA62 results, is BMI=(0.965±0.63)×10−6. The combined branching ratio in the full kinematic range assuming a ChPT description is BChPT=(1.003±0.056)×10−6. The uncertainties are dominated by the statistical errors. The data support the ChPT prediction for a cusp in the di-photon invariant mass spectrum at the two pion threshold and are in agreement with both O(p4) and O(p6) ChPT predictions.