Observation of the Radiative Decay D_{s0}^{*}(2317)^{+}→D_{s}^{*+}γ

We report the first observation of the radiative decay D_{s0}^{*}(2317)^{+}→D_{s}^{*+}γ with a statistical significance exceeding 10 standard deviations. The signal is observed in the continuum e^{+}e^{-}→cc[over ¯] process, using combined data samples of 980.4  fb^{-1} from Belle and 427.9  fb^{-1} from Belle II, collected at the KEKB and SuperKEKB asymmetric-energy e^{+}e^{-} colliders, respectively. The branching fraction ratio B[D_{s0}^{*}(2317)^{+}→D_{s}^{*+}γ]/B[D_{s0}^{*}(2317)^{+}→D_{s}^{+}π^{0}] is measured to be [7.13±0.70(stat)±0.26(syst)]%. This result provides crucial discrimination between theoretical models of the D_{s0}^{*}(2317)^{+} structure.