Measurement of K+→π0μ+νγ decay using stopped kaons

The K+→π0μ+νγ (Kμ3γ) decay has been measured with stopped positive kaons at the KEK 12 GeV proton synchrotron. A Kμ3γ sample containing 125 events was obtained. The partial branching ratio Br(Kμ3γ,Eγ>30MeV,θμ+γ>20°) was found to be [2.4±0.5(stat)±0.6(syst)]×10−5, which is in good agreement with theoretical predictions.