Rare H and Z decays to quarkonia with CMS

Abstract

Searches for SM Higgs and Z bosons decaying to a J/ψ and a photon, with subsequent decay of the J/ψ to µ+µ− and the Z boson rare decay to a ψ meson and two oppositely charged same-flavour leptons, ℓ+ℓ−, where ψ represents contributions from direct J/ψ and ψ(2S) → J/ψ X, and ℓ = µ, e are presented. The analyses are performed using data recorded by the CMS detector from proton-proton collisions at center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb−1. The observed (expected) upper limit on the branching fraction for H → J/ψγ with mH = 125 GeV is 7.6(5.2) × 10−4, 260 (170) times larger than the standard model prediction, at 95% confidence level. The observed (expected) upper limit on the Z → J/ψγ branching fraction is 1.4(1.6)×10−6, 15 (18) times larger than the standard model prediction, at 95% confidence level. The signal of the Z boson rare decay to a ψ meson and two oppositely charged same-flavour leptons, ℓ+ℓ−, is observed with a significance in excess of 5 standard deviations. After removing the contributions from ψ(2S) decays to J/ψ, the ratio of the branching fraction of the Z → J/ψℓ+ℓ−, to the decay Z → µ+µ−µ+µ− within a fiducial phase space is measured to be