Three rare decay processes of the Higgs boson to a ρ(770) 0, φ(1020), or K ∗ (892) 0 meson and a photon are searched for using √s = 13 TeV proton-proton collision data collected by the CMS experiment at the LHC. Events are selected assuming the mesons decay into a pair of charged pions, a pair of charged kaons, or a charged kaon and pion, respectively. Depending on the Higgs boson production mode, different triggering and reconstruction techniques are adopted. The analyzed data sets correspond to integrated luminosities up to 138 fb−1, depending on the reconstructed final state. After combining various data sets and categories, no significant excess above the background expectations is observed. Upper limits at 95% confidence level on the Higgs boson branching fractions into ρ(770) 0γ, φ(1020)γ, and K ∗ (892) 0γ are determined to be 3.7 × 10−4, 3.0 × 10−4, and 3.0 × 10−4, respectively. In case of the ρ(770) 0γ and φ(1020)γ channels, these are the most stringent experimental limits to date.
