Search for the rare decay D${}^0$ $\to$ ${\mu }^{+}{\mu }^{-}$ in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV

A search for the rare decay D${}^0$ $\to$ ${\mu }^{+}{\mu }^{-}$ is reported using proton-proton collision events at $\sqrt{s}$ = 13.6 TeV collected by the CMS detector in 2022$-$2023, corresponding to an integrated luminosity of 64.5 fb${}^{-1}$. This is the first analysis to use a newly developed inclusive dimuon trigger, expanding the scope of the CMS flavor physics program. The search uses D${}^0$ mesons obtained from D${}^{\ast +}$ $\to$ D${}^0{\pi }^{+}$ decays. No significant excess is observed. A limit on the branching fraction of $\mathcal{B}$(D${}^0$ $\to$ ${\mu }^{+}{\mu }^{-}$) $<$ 2.4 $\times$ 10${}^{-9}$ at 95% confidence level is set. This is the most stringent upper limit set on any flavor changing neutral current decay in the charm sector.