Rare Z and H Decays to Quarkonia

Rare decay modes of the Z and Higgs bosons involving the production of quarkonium states offer a very clean experimental signature. A search for the Z and H decays to final states with a $J/\psi$ meson and a photon, and the rare Z decay to a lepton pair and a vector meson is performed using data collected by the CMS experiment. The Z boson decay to a $J/\psi$ meson and two oppositely charged same-flavor leptons is observed for the first time. The measurement of this particular branching fraction can be valuable for the calculation of the fragmentation function for a virtual lepton to split into a $J/\psi$ meson, as well as for the evaluation of potential backgrounds to Higgs boson decays into quarkonia or searches for new physics. The measurements presented utilize a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9~$\textrm{fb}^{-1}$.