The dark axion portal provides a well-motivated framework for new physics beyond the Standard Model, in which an axionlike particle (ALP) couples simultaneously to a photon and a dark photon, leading to distinctive collider signatures. In this work, we investigate the sensitivity to the $a\text{−}\gamma \text{−}{\gamma }^{\prime }$ interaction via the mono-photon channel arising from ${\mu }^{+}{\mu }^{-}\to a{\gamma }^{\prime }$ with $a\to \gamma {\gamma }^{\prime }$ at the 1.5 TeV muon collider with an integrated luminosity of $\mathcal{L}=500{\mathrm{fb}}^{-1}$ for the polarized and unpolarized beam configurations, $P({\mu }^{+},{\mu }^{-})=(-100\%,+100\%)$ and $P({\mu }^{+},{\mu }^{-})=(0,0)$, using detector-level simulation. The signal is characterized by a single energetic photon accompanied by missing energy as the dark photons escape detection. The projected sensitivity reaches the $\mathcal{O}({10}^{-5}){\mathrm{GeV}}^{-1}$ level for ALP masses in the range $1\mathrm{GeV}\le m_a\le 1200\mathrm{GeV}$ for $P({\mu }^{+},{\mu }^{-})=(-100\%,+100\%)$, while for $P({\mu }^{+},{\mu }^{-})=(0,0)$ the projected sensitivity reaches the $\mathcal{O}({10}^{-4}){\mathrm{GeV}}^{-1}$ level for the same ALP mass range. These results demonstrate that the mono-photon signature at a muon collider provides a sensitive probe of the $a\text{−}\gamma \text{−}{\gamma }^{\prime }$ interaction over a wide mass range.

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• Phenomenology
• Axion-like particles
• Monte Carlo methods