Search for the decay K+ to pi+ gamma gamma in the pi+ momentum region P>213 MeV/c

TL;DR

This paper reports a search for the rare decay K+ to pi+ gamma gamma in a specific momentum region, setting upper limits on its branching ratio and also constraining the simpler K+ to pi+ gamma decay.

Contribution

The study provides the first upper limit on the K+ to pi+ gamma gamma decay in the high-momentum region, using data to improve constraints on rare kaon decay modes.

Findings

No events observed for K+ to pi+ gamma gamma decay.

Upper limit on B(K+ to pi+ gamma gamma, P>213 MeV/c) < 8.3 x 10^-9.

Upper limit on B(K+ to pi+ gamma) < 2.3 x 10^-9.

Abstract

We have searched for the K+ to pi+ gamma gamma decay in the kinematic region with pi+ 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+ to pi+ gamma gamma, P>213 MeV/c) < 8.3 x 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+ to pi+ gamma branching ratio of 2.3 x 10-9 at the 90% confidence level.