Study of the K+- to pi+- gamma gamma decay by the NA62 experiment.

A study of the dynamics of the rare decay K±→π±γγK±→π±γγ has been performed on a sample of 232 decay candidates, with an estimated background of 17.4±1.117.4±1.1 events, collected by the NA62 experiment at CERN in 2007. The results are combined with those from a measurement conducted by the NA48/2 Collaboration at CERN. The combined model-independent branching ratio in the kinematic range z=(mγγ/mK)2>0.2z=(mγγ/mK)2>0.2 is BMI(z>0.2)=(0.965±0.063)×10−6BMI(z>0.2)=(0.965±0.063)×10−6, and the combined branching ratio in the full kinematic range assuming a Chiral Perturbation Theory description is B(Kπγγ)=(1.003±0.056)×10−6B(Kπγγ)=(1.003±0.056)×10−6. A detailed comparison of the results with the previous measurements is performed.