A new measurement of the $K^{\pm }\to {\pi }^{\pm }\gamma \gamma$ decay at the NA48/2 experiment

Abstract

The NA48/2 experiment at CERN collected two data samples with minimum bias trigger conditions in 2003 and 2004. A measurement of the rate and dynamic properties of the rare decay $K^{\pm }\to {\pi }^{\pm }\gamma \gamma$ from these data sets based on 149 decay candidates with an estimated background of $15.5\pm 0.7$ events is reported. The model-independent branching ratio in the kinematic range $z=(m_{\gamma \gamma }/m_K{)}^2>0.2$ is measured to be ${\mathcal{B}}_{\mathrm{MI}}(z>0.2)=(0.877\pm 0.089)\times 10^{-6}$, and the branching ratio in the full kinematic range assuming a particular Chiral Perturbation Theory description to be $\mathcal{B}(K_{\pi \gamma \gamma })=(0.910\pm 0.075)\times 10^{-6}$.

arXiv commentA revised version accepted for publication by Physics Letters B