Search for the decay K+→π+γγ in the π+ momentum region P>213MeV/c

We have searched for the K+→π+γγ decay in the kinematic region with π+ momentum close to the end point. No events were observed, and the 90% confidence-level upper limit on the partial branching ratio was obtained, B(K+→π+γγ,P>213MeV/c)<8.3×10−9 under the assumption of chiral perturbation theory including next-to-leading order “unitarity” corrections. The same data were used to determine an upper limit on the K+→π+γ branching ratio of 2.3×10−9 at the 90% confidence level.