New result on the measurement of the direct photon emission in K+ --> pi^+ pi^0 gamma decay

TL;DR

This paper reports a new measurement of the direct photon emission in K+ --> pi+ pi0 gamma decay using stopped kaons, providing a branching ratio with statistical and systematic uncertainties.

Contribution

It presents the first precise measurement of the direct photon emission branching ratio in this decay mode with a large event sample.

Findings

Branching ratio for direct photon emission: (3.8 ± 1.1) x 10^{-6}

Decay spectrum fitted with 10,000 events

Assumption of no interference component in the analysis

Abstract

We present a new result on the K^+ --> pi^+ pi^0 gamma decay measurement using stopped kaons. The best fit to the decay spectrum comprised of 10k events gives a branching ratio for the direct photon emission of [3.8+-0.8(stat)+-0.7(syst)] times 10^{-6} in the pi^+ kinetic energy region of 55 to 90 MeV. This result has been obtained with the assumption that there is no component due to interference with the inner bremsstrahlung.