CMS-HIG-18-025

CMS-HIG-18-025 ; CERN-EP-2019-082
Search for Higgs and Z boson decays to $\mathrm{J}/\psi$ or $\Upsilon$ pairs in proton-proton collisions at $\sqrt{s} = $ 13 TeV
CMS Collaboration
24 May 2019
Phys. Lett. B 797 (2019) 134811
Abstract: A search for decays of the Higgs and Z boson to pairs of $\mathrm{J}/\psi$ or $\Upsilon(\text{nS})$ (n=1,2,3) mesons, with their subsequent decay to $\mu^{+}\mu^{-}$ pairs, is presented. The analysis uses data from proton-proton collisions at $\sqrt{s} = $ 13 TeV, collected with the CMS detector at the LHC in 2017 and corresponding to an integrated luminosity of 37.5 fb$^{-1}$. While an observation of such a decay with this sample would indicate the presence of physics beyond the standard model, no significant excess is observed. Upper limits at 95% confidence level are placed on the branching fractions of these decays. In the $\mathrm{J}/\psi$ pair channel, the limits are $ 1.8 \times 10^{-3} $ and $ 2.2 \times 10^{-6} $ for the Higgs and Z boson, respectively, while in the combined $\Upsilon(\text{nS})$ pair channel, the limits are $ 1.4 \times 10^{-3} $ and $ 1.5 \times 10^{-6} $, respectively, when the mesons from the Higgs and Z boson decay are assumed to be unpolarized. When fully longitudinal and transverse polarizations are considered the limits reduce by about 22-29% and increase by about 10-13%, respectively.
Links: e-print arXiv:1905.10408 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The three leftmost plots show Feynman diagrams for $\mathrm{H} \to \text {QQ}$ with Q = charmonium or bottomonium states according to Ref. [14]. In the two leftmost diagrams, the virtual particles are Z bosons. In center-right diagram, quarks are the main contribution to the loops and the virtual particles are either photons or gluons. In the latter case additional soft-gluon exchange occurs. The rightmost diagram shows the leading order $\mathrm{Z} \to \text {QQ}$ decay diagram according to Ref. [15].
png pdf	Figure 1-a: Feynman diagram for $\mathrm{H} \to \text {QQ}$ with Q = charmonium or bottomonium states according to Ref. [14]. The virtual particles are Z bosons.
png pdf	Figure 1-b: Feynman diagram for $\mathrm{H} \to \text {QQ}$ with Q = charmonium or bottomonium states according to Ref. [14]. The virtual particles are Z bosons.
png pdf	Figure 1-c: Feynman diagram for $\mathrm{H} \to \text {QQ}$ with Q = charmonium or bottomonium states according to Ref. [14]. Quarks are the main contribution to the loops and the virtual particles are either photons or gluons. In the latter case additional soft-gluon exchange occurs.
png pdf	Figure 1-d: Feynman diagram for the leading order $\mathrm{Z} \to \text {QQ}$ decay according to Ref. [15].
png pdf	Figure 2: The four-muon invariant mass distributions, for ${\mathrm{J}/\psi} {\mathrm{J}/\psi} $ (left) and $\Upsilon \Upsilon $ (right) candidates (error bars for zero entries are omitted). The result of the maximum likelihood fit is superimposed (solid blue line). For illustrative purposes, the plots also show the distributions for simulated Higgs and Z boson signals (dashed red lines), each normalized to two events.
png pdf	Figure 2-a: The four-muon invariant mass distribution, for ${\mathrm{J}/\psi} {\mathrm{J}/\psi} $ candidates (error bars for zero entries are omitted). The result of the maximum likelihood fit is superimposed (solid blue line). For illustrative purposes, the plot also shows the distributions for simulated Higgs and Z boson signals (dashed red lines), each normalized to two events.
png pdf	Figure 2-b: The four-muon invariant mass distribution, for $\Upsilon \Upsilon $ candidates (error bars for zero entries are omitted). The result of the maximum likelihood fit is superimposed (solid blue line). For illustrative purposes, the plot also shows the distributions for simulated Higgs and Z boson signals (dashed red lines), each normalized to two events.

Tables
png pdf	Table 1: Exclusion limits at 95% CL for the branching fractions of the H and Z boson decays to ${\mathrm{J}/\psi} $ or $\Upsilon $ mesons pairs. The second column lists the observed limits. The third column shows the median expected limits with the upper and lower bounds in the expected 68% CL intervals.

Summary

In summary, this Letter presents the first search for decays of the Higgs and Z boson to pairs of $\mathrm{J}/\psi$ or $\Upsilon(\text{nS})$ (n=1,2,3) mesons, with their subsequent decay to $\mu^{+}\mu^{-}$ pairs. Data from pp collisions at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 37.5 fb$^{-1}$ are used. No excess has been observed above a small background in the $\mathrm{J}/\psi$ pair and with vanishingly small background in the $\Upsilon$ pair channels. The observed upper limits at 95% confidence level on the branching fractions for the Higgs boson decays for unpolarized mesons are $\mathcal{B}(\mathrm{H}\to\mathrm{J}/\psi \mathrm{J}/\psi) < 1.8\times 10^{-3}$ and $\mathcal{B}(\mathrm{H}\to\Upsilon \Upsilon) < 1.4\times 10^{-3}$. The observed upper limits on the branching fractions for the Z boson decay in the unpolarized scenario are $\mathcal{B}(\mathrm{Z}\to\mathrm{J}/\psi \mathrm{J}/\psi) < 2.2\times 10^{-6}$ and $\mathcal{B}(\mathrm{Z}\to\Upsilon \Upsilon) < 1.5\times 10^{-6}$, where all three $\Upsilon(\text{nS})$ states are considered. Extreme polarization scenarios give rise to variations in the observed boson decay branching fractions between $-$(22-29)% for fully longitudinally polarized $\mathrm{J}/\psi$ and $\Upsilon$ mesons and $+$(10-13)% for fully transversely polarized mesons.

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