Measurement of the K + →π 0 μ + ν μ γ branching ratio

A measurement of the decay K + → π 0 μ + v μ γ has been performed with the E787 detector at Brookhaven National Laboratory. Forty events were observed in the signal region with the background expectation of (16.5 ± 2.7) events. The branching ratio was measured to be (1.58 ± 0.46(stat.) ± 0.08(syst.)) X 10-- 5 in the kinematic region E γ > 30 MeV and θ μγ > 20°, where E γ is the energy of the emitted photon and θ μγ is the angle between the muon and the photon in the K + rest frame. The results were consistent with theoretical predictions.