Observation of the radiative decay $D_s (2317)^+ \to D_s^* \gamma$

TL;DR

This paper reports the first observation of the radiative decay of the $D_s(2317)^+$ meson with high significance, measuring its branching ratio relative to the dominant decay mode, providing new insights into its quark structure.

Contribution

The first experimental observation of the decay $D_s(2317)^+ o D_s^* o ext{gamma}$ with a precise measurement of its branching ratio relative to $D_s^+ o ext{pi}^0$, using large datasets from Belle and Belle II.

Findings

Decay observed with >10 sigma significance.

Branching ratio ratio measured as 7.14% with uncertainties.

Provides new experimental input on the quark structure of $D_s(2317)^+$.

Abstract

We observe the radiative decay $D^{*}_{s0}(2317)^{+} \to D_{s}^{*+} \gamma$ for the first time, with a significance exceeding $10$ standard deviations. The signal is found in the continuum $e^+ e^- \to c\bar{c}$ process with the combined data samples of 980.4~$\rm fb^{-1}$ and 427.9~$\rm fb^{-1}$ collected by the Belle and Belle~II detectors operating at the KEKB and SuperKEKB asymmetric-energy $e^+e^-$ colliders, respectively. The branching fraction ratio ${\cal B}(D^{*}_{s0}(2317)^{+} \to D_{s}^{*+} \gamma)/{\cal B}(D^{*}_{s0}(2317)^{+} \to D_{s}^{+} \pi^{0})$ is measured to be $[7.14 \pm 0.70({\rm stat.}) \pm 0.23({\rm syst.})]\%$. This result provides significant new experimental input for the determination of the quark structure of the $D^{*}_{s0}(2317)^{+}$, which remains unknown.