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

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,${\mathrm{f}\mathrm{b}}^{-1}$ 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 $\mathcal{B}(D^0\to \gamma \omega )=(2.12\pm {0.40}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}}\pm {0.25}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}})\times {10}^{-5}$ 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.