Search for rare decays of Z and Higgs bosons to J/psi and a photon in proton-proton collisions at sqrt(s) = 13 TeV

A search is presented for decays of \mathrm {Z} and Higgs bosons to a {\mathrm {J}/\psi } meson and a photon, with the subsequent decay of the {\mathrm {J}/\psi } to \mathrm {\mu ^+}\mathrm {\mu ^-} . The analysis uses data from proton-proton collisions with an integrated luminosity of 35.9\,\text {fb}^{-1} at \sqrt{s}=13\,\text {TeV} collected with the CMS detector at the LHC. The observed limit on the \mathrm {Z}\rightarrow {\mathrm {J}/\psi } \gamma decay branching fraction, assuming that the {\mathrm {J}/\psi } meson is produced unpolarized, is 1.4\times 10^{-6} at 95% confidence level, which corresponds to a rate higher than expected in the standard model by a factor of 15. For extreme-polarization scenarios, the observed limit changes from -13.6 to +8.6\% with respect to the unpolarized scenario. The observed upper limit on the branching fraction for \mathrm {H} \rightarrow {\mathrm {J}/\psi } \gamma where the {\mathrm {J}/\psi } meson is assumed to be transversely polarized is 7.6\times 10^{-4}, a factor of 260 larger than the standard model prediction. The results for the Higgs boson are combined with previous data from proton-proton collisions at \sqrt{s}=8\,\text {TeV} to produce an observed upper limit on the branching fraction for \mathrm {H} \rightarrow {\mathrm {J}/\psi } \gamma that is a factor of 220 larger than the standard model value.