Rare exclusive decays of the Z boson revisited

The realization that first- and second-generation Yukawa couplings can be probed by decays of the Higgs boson to a meson in association with a photon has renewed interest in such rare exclusive decays. We present here a detailed study of the rare Z-boson processes Z→J/ψ+γ, Z→ +γ, and Z→φ+γ that can serve as benchmarks for the analogous Higgs-boson decays. We include both direct-production and fragmentation contributions to these decays and consider the leading QCD corrections and the relativistic corrections to the J/ψ and processes. We present numerical predictions for the branching ratios that include a careful accounting of the theoretical uncertainties.