Evidence for Direct Emission in the DecayK±→π±π0γ

Abstract

We have obtained about 4000 events above background which satisfy the two-constraint fit with the hypothesis $K^{\pm }\to {\pi }^{\pm }{\pi }^0\gamma$. Their Dalitz-plot population shows the existence of direct radiation in addition to that of the expected inner bremsstrahlung. The best fit to the sum of $K^{+}$ and $K^{-}$ decays in the charged-pion kinetic energy interval of 55 to 90 MeV gives a branching ratio for direct emission of (1.56 ± 0.35) × ${10}^{-5\mathrm{}}$, with a systematic uncertainty of ± 0.5 × ${10}^{-5\mathrm{}}$. No interference is required for a good fit.