Rare H and Z decays to quarkonia with CMS

Eliza Melo Da Costa
2018 Journal of Physics, Conference Series  
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, + − , where ψ represents contributions from direct J/ψ and ψ(2S) → J/ψ X, and = µ, e are presented. The analyses are performed using data recorded by the CMS detector from protonproton collisions at center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 f b −1 . The
more » ... f b −1 . The observed (expected) upper limit on the branching fraction for H → J/ψγ with m H = 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, + − , 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/ψ + − , to the decay Z → µ + µ − µ + µ − within a fiducial phase space is measured to be 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, + − , where ψ represents contributions from direct J/ψ and ψ(2S) → J/ψ X, and = 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 f b −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, + − , 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/ψ + − , to the decay Z → µ + µ − µ + µ − within a fiducial phase space is measured to be B(Z → J/ψ + − ) B(Z → µ + µ − µ + µ − ) = 0.70 ± 0.18 (stat) ± 0.05 (syst).
doi:10.1088/1742-6596/1137/1/012013 fatcat:l4ggqrqebzgnlam335ldxqwh3m