Study of the radiative decayK+→μ+νγ

The radiative decay $K^{+}$→${\mu }^{+}$νγ has been studied by a high-resolution magnetic spectrometer combined with a NaI(Tl) photon detector system. The momentum spectrum of muon from this decay mode was measured in the region 214.5<$p_{\mu }$<231.5 MeV/c. The observed partial decay rate of the radiative decay in this region agreed with the QED calculation within the error of 3%. The structure-dependent components of the decay were studied and new values of the form factors were obtained as ‖$F_V$+$F_A$ ${\Vert }_{\left(\mu \right)}$ $M_K$<0.23, -2.5<($F_V$-$F_A$ ${)}_{\left(\mu \right)}$ $M_K$<0.3. By using these bounds the branching ratio was determined as B($K_{\mu \nu \gamma }$,$p_{\mu }$<231.5 MeV/c)=(5.4±0.3)×${10}^{\mathrm{-}3}$.