Study of the rare decay $K^{\pm} → \pi^{\pm}γγ$ in the NA48/2 and NA62 experiments at CERN

A sample of about 300 K ! rare decays with a background contamination below 10% has been collected by the NA48/2 and NA62 experiments at CERN during low intensity runs with minimum bias trigger conguration. The measurements of the decay spectrum and rate provide a crucial test of the Chiral Perturbation Theory (ChPT) describing weak processes at low energy