Study of the $K^{\pm }\to {\pi }^{\pm }\gamma \gamma$ decay by the NA62 experiment

A study of the dynamics of the rare decay $K^{\pm }\to {\pi }^{\pm }\gamma \gamma$ has been performed on a sample of 232 decay candidates, with an estimated background of $17.4\pm 1.1$ 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 $z=(m_{\gamma \gamma }\mathrm{/}{m}_K{)}^2>0.2$ is ${\cal B}{\rm MI}(z>0.2) = (0.965 \pm 0.063) \times 10^{-6}$, and the combined branching ratio in the full kinematic range assuming a Chiral Perturbation Theory description is ${\cal B}(K{\pi\gamma\gamma}) = (1.003 \pm 0.056) \times 10^{-6}$. A detailed comparison of the results with the previous measurements is performed.