First Observation of the Radiative Decay $D^0\to \gamma \omega$

Abstract

We report the first observation of the radiative charm decay $D^0\to \gamma \omega$ with a significance of $6.0\sigma$. The analysis uses 20.3\,${\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected by the BESIII detector at a center-of-mass energy of 3.773\,GeV, and employs a deep learning strategy based on the Particle Transformer architecture. The absolute branching fraction of $\mathcal{B}(D^0\to \gamma \omega )=(2.12\pm 0.40_{\mathrm{stat}}\pm 0.25_{\mathrm{syst}})\times 10^{-5}$ confirms the dominance of long-distance hadronic dynamics in radiative charm decays and provides a valuable benchmark for testing non-perturbative QCD calculations of $D\to \gamma V$ transitions.