Search for rare decays of $$\mathrm {}$$ and Higgs bosons to $${\mathrm {J}/\psi } $$J/ψ and a photon in proton-proton collisions at $$\sqrt{s}$$s = 13$$\,\text {TeV}$$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.