CMS-PAS-HIG-18-025

CMS-PAS-HIG-18-025
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
March 2019

Abstract: A search is presented for decays of the Higgs and Z boson to pairs of $\mathrm{J}/\psi$ or $\Upsilon(n\mathrm{S})$ ( $n=$ 1, 2, 3), with the subsequent decay of the mesons to $\mu^+\mu^-$ . The analysis uses data from proton-proton collisions with an integrated luminosity of 37.5 fb $^{-1}$ at $\sqrt{s}=$ 13 TeV collected with the CMS detector at the LHC in 2017. An observation of such a decay with this sample would indicate the presence of physics beyond the standard model. No significant excess of events is observed and 95% confidence level upper limits are placed on the branching fractions. In the $\mathrm{J}/\psi$ pair final state 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 $\Upsilon(n\mathrm{S})$ pair final states the limits are 1.4 $\times 10^{-3}$ and 1.5 $\times 10^{-6}$ , respectively. The $\mathrm{J}/\psi$ and $\Upsilon(n\mathrm{S})$ mesons from the Higgs and Z decay are assumed unpolarized. With longitudinally polarized $\mathrm{J}/\psi$ and $\Upsilon$ mesons in the Higgs and Z decay the upper limits reduce by about 22-29%, while with transversely polarized mesons the decay limits increase by about 10-13%.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 797 (2019) 134811. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Feynman diagrams for ${\mathrm {H}} \to \mathrm{Q} \mathrm{Q}$ decays with $\mathrm{Q}= {{\mathrm {J}/\psi}}$ or $\Upsilon$ . In diagram (a) the quarks are the main contribution to the loop and the virtual particles are either photons or gluons. In the latter case additional soft gluon exchange occurs. In diagram (b) the virtual particles are Z, in (c) they are either Z, W, or gluons.
png pdf	Figure 1-a: Feynman diagram for ${\mathrm {H}} \to \mathrm{Q} \mathrm{Q}$ decays with $\mathrm{Q}= {{\mathrm {J}/\psi}}$ or $\Upsilon$ . The quarks are the main contribution to the loop and the virtual particles are either photons or gluons. In the latter case additional soft gluon exchange occurs.
png pdf	Figure 1-b: Feynman diagram for ${\mathrm {H}} \to \mathrm{Q} \mathrm{Q}$ decays with $\mathrm{Q}= {{\mathrm {J}/\psi}}$ or $\Upsilon$ . The virtual particles are Z bosons.
png pdf	Figure 1-c: Feynman diagram for ${\mathrm {H}} \to \mathrm{Q} \mathrm{Q}$ decays with $\mathrm{Q}= {{\mathrm {J}/\psi}}$ or $\Upsilon$ . The virtual particles are either Z, W, or gluons.
png pdf	Figure 2: The four-muon invariant mass distributions, for ${{\mathrm {J}/\psi}} {{\mathrm {J}/\psi}}$ candidates (left) and $\Upsilon \Upsilon$ candidates (right). The result of the maximum likelihood fit is superimposed (solid blue line). For demonstration purpose the plots also show two simulated signal events for Z and Higgs boson (dashed red lines).
png pdf	Figure 2-a: The four-muon invariant mass distributions, for ${{\mathrm {J}/\psi}} {{\mathrm {J}/\psi}}$ candidates. The result of the maximum likelihood fit is superimposed (solid blue line). For demonstration purpose the plot also shows two simulated signal events for Z and Higgs boson (dashed red lines).
png pdf	Figure 2-b: The four-muon invariant mass distributions, for $\Upsilon \Upsilon$ candidates. The result of the maximum likelihood fit is superimposed (solid blue line). For demonstration purpose the plot also shows two simulated signal events for Z and Higgs boson (dashed red lines).

Tables
png pdf	Table 1: Exclusion limits at 95% CL for the branching fractions of H and Z boson decays to ${{\mathrm {J}/\psi}}$ or $\Upsilon$ 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, the paper presents the first search for Higgs and Z boson decays into

$\mathrm{J}/\psi$ or

$\Upsilon$ meson pairs with the mesons subsequently decaying into

$\mu^{+}\mu^{-}$ . Data from pp collisions at

$\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 37.5 fb

$^{-1}$ is used. No excess has been observed above a small background in the

$\mathrm{J}/\psi$ pair and with no background in the

$\Upsilon$ pair final state. The observed upper limits at 95% confidence level on the branching fractions for the Higgs boson decays for unpolarized mesons are set at

$\mathcal{B}(\mathrm{H} \to \mathrm{J}/\psi \mathrm{J}/\psi) < 1.8 \times 10^{-3}$ and

$\mathcal{B}(\mathrm{H} \to \Upsilon \Upsilon) < 1.4 \times 10^{-3}$ . The corresponding observed upper limits on the Bs for the Z boson decay in the unpolarized scenario are set at

$\mathcal{B}(\mathrm{Z} \to \mathrm{J}/\psi \mathrm{J}/\psi) < 2.2 \times 10^{-6}$ and

$\mathcal{B}(\mathrm{H} \to \Upsilon \Upsilon) < 1.5 \times 10^{-6}$ where all three

$\Upsilon(n\text{S})$ states are considered. Extreme polarization scenarios give rise to variations in the observed boson decay Bs from

$-$ (22-29)% for fully longitudinally polarized

$\mathrm{J}/\psi$ and

$\Upsilon$ mesons and

$+$ (10-13)% for fully transversely polarized mesons. The analysis is expected to motivate renewed calculations of the Higgs branching fractions in the SM as only few signal events could measure the presence of BSM physics.

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