Search for rare decays of the Higgs boson into a photon and a $\rho$, $\phi$ or $K^{∗0}$ meson with the CMS experiment

Higgs-boson decays into a photon and a $\rho$(770), $\phi$(1020), or $\Kstar$ (892) meson are searched for using proton-proton collision data collected by the CMS experiment at the LHC at $\sqrt{s}=13$ TeV. Events are selected in which the mesons decay into pairs of charged pions, pairs of charged kaons, and charged kaon-pion pairs respectively. Depending on the Higgs-boson production mode, different signal triggering and reconstruction techniques are adopted. The analysed data sets correspond to an integrated luminosity varying between 40 and 137 $\fbinv$, depending on the detailed final state. By combining these production modes, no significant excess above the background expectations is observed in any search channel. Upper limits at the 95 \% confidence level on the Higgs boson branching fractions into $\RhoGamma$, $\PhiGamma$, and $\KstarGamma$ are determined to be $3.74 \cdot 10^{-4}$, $2.97 \cdot 10^{-4}$, and $1.71 \cdot 10^{-4}$, respectively. These results constitute the most stringent experimental limits to date on the aforementioned decay channels.