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| CMS-HIG-20-008 ; CERN-EP-2022-074 | ||
| Search for Higgs boson decays into Z and J/$\psi$ and for Higgs and Z boson decays into J/$\psi$ or $\Upsilon$ pairs in pp collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 7 June 2022 | ||
| Phys. Lett. B 842 (2023) 137534 | ||
| Abstract: Decays of the Higgs boson into a Z boson and a J/$\psi$ or $\psi(\text{2S})$ meson are searched for in four-lepton final states with the CMS detector at the LHC. A data set of proton-proton collisions corresponding to an integrated luminosity of 138 fb$^{-1}$ is used. Using the same data set, decays of the Higgs and Z boson into quarkonium pairs are also searched for. An observation of such decays with this sample would indicate the presence of physics beyond the standard model. No evidence for these decays has been observed and upper limits at the 95% confidence level are placed on the corresponding branching fractions ($\mathcal{B}$). Assuming longitudinal polarization of the Higgs boson decay products, 95% confidence level observed upper limits for $\mathcal{B}(\mathrm{H}\to\mathrm{Z}\mathrm{J}/\psi)$ and $\mathcal{B}(\mathrm{H}\to\mathrm{Z}\psi(\text{2S}))$ are 1.9 $\times$ 10$^{-3}$ and 6.6 $\times$ 10$^{-3}$, respectively. | ||
| Links: e-print arXiv:2206.03525 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Sample Feynman diagrams depicting direct (left) and indirect (middle, right) quark coupling contributions to the $\mathrm{H} \to \mathrm{Z} \mathrm {Q}$ decay, where $\mathrm {Q}$ represents a quarkonium and $\mathrm {q}$ is a quark. The diagrams represent Higgs boson decays into quarkonium pairs when replacing the bottom section with the upper half in each. |
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Figure 1-a:
Sample Feynman diagram depicting direct quark coupling contributions to the $\mathrm{H} \to \mathrm{Z} \mathrm {Q}$ decay, where $\mathrm {Q}$ represents a quarkonium and $\mathrm {q}$ is a quark. |
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Figure 1-b:
Sample Feynman diagram depicting indirect quark coupling contributions to the $\mathrm{H} \to \mathrm{Z} \mathrm {Q}$ decay, where $\mathrm {Q}$ represents a quarkonium and $\mathrm {q}$ is a quark. |
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Figure 1-c:
Sample Feynman diagram depicting indirect quark coupling contributions to the $\mathrm{H} \to \mathrm{Z} \mathrm {Q}$ decay, where $\mathrm {Q}$ represents a quarkonium and $\mathrm {q}$ is a quark. |
png pdf |
Figure 2:
Four-lepton invariant mass distributions, (left) for $\mathrm{Z} {\mathrm{J}/\psi} \to 4\mu $ candidates and (right) for $\mathrm{Z} {\mathrm{J}/\psi} \to 2\mathrm{e} 2\mu $ candidates. The result of the maximum likelihood fit to the background (Bkg) is superimposed (solid blue line). For illustrative purposes, the plots show simulated $\mathrm{H} \to \mathrm{Z} {\mathrm{J}/\psi} $ (dashed red line) and $\mathrm{H} \to \mathrm{Z} \psi(\text{2S})$ (dotted magenta line) signals normalized to their observed upper limit branching fractions at 95% CL as obtained in this analysis, where $\psi(\text{2S})$ decays into ${\mathrm{J}/\psi} $+X. |
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Figure 2-a:
Four-lepton invariant mass distribution for $\mathrm{Z} {\mathrm{J}/\psi} \to 4\mu $ candidates. The result of the maximum likelihood fit to the background (Bkg) is superimposed (solid blue line). For illustrative purposes, the plot shows simulated $\mathrm{H} \to \mathrm{Z} {\mathrm{J}/\psi} $ (dashed red line) and $\mathrm{H} \to \mathrm{Z} \psi(\text{2S})$ (dotted magenta line) signals normalized to their observed upper limit branching fractions at 95% CL as obtained in this analysis, where $\psi(\text{2S})$ decays into ${\mathrm{J}/\psi} $+X. |
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Figure 2-b:
Four-lepton invariant mass distribution for $\mathrm{Z} {\mathrm{J}/\psi} \to 2\mathrm{e} 2\mu $ candidates. The result of the maximum likelihood fit to the background (Bkg) is superimposed (solid blue line). For illustrative purposes, the plot shows simulated $\mathrm{H} \to \mathrm{Z} {\mathrm{J}/\psi} $ (dashed red line) and $\mathrm{H} \to \mathrm{Z} \psi(\text{2S})$ (dotted magenta line) signals normalized to their observed upper limit branching fractions at 95% CL as obtained in this analysis, where $\psi(\text{2S})$ decays into ${\mathrm{J}/\psi} $+X. |
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Figure 3:
The four-muon invariant mass distribution of ${\mathrm{J}/\psi} {\mathrm{J}/\psi} $ candidates (error bars for empty bins are not shown). The result of the maximum likelihood fit to the background (Bkg) is superimposed (solid blue line). For illustrative purposes, the plots show the distributions for simulated signals of the Higgs and Z boson decaying into ${\mathrm{J}/\psi} {\mathrm{J}/\psi} $ (dashed and dashed-dotted red lines). The signals for the Higgs boson decays $\mathrm{H} \to \psi(\text{2S}){\mathrm{J}/\psi} $ (dotted magenta line) and $\mathrm{H} \to \psi(\text{2S})\psi(\text{2S})$ (dashed-dotted black line) are also shown, where $\psi(\text{2S})$ decays into ${\mathrm{J}/\psi}$. Each signal is normalized to their observed 95% CL upper limit branching fraction from this analysis. |
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Figure 4:
The four-muon invariant mass distributions for $\Upsilon(\text{nS})\Upsilon(\text{mS})$ (left) and $\Upsilon(\text{1S})\Upsilon(\text{1S})$ (right) candidates (error bars for empty bins are not shown). The result of the maximum likelihood fit to background (Bkg) is superimposed (solid blue line). For illustrative purposes, the plots show the distributions for simulated Higgs and Z boson signals (dashed and dashed-dotted red lines) normalized to their observed 95% CL upper limit branching fractions from this analysis. |
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Figure 4-a:
The four-muon invariant mass distribution for $\Upsilon(\text{nS})\Upsilon(\text{mS})$ candidates (error bars for empty bins are not shown). The result of the maximum likelihood fit to background (Bkg) is superimposed (solid blue line). For illustrative purposes, the plot shows the distributions for simulated Higgs and Z boson signals (dashed and dashed-dotted red lines) normalized to their observed 95% CL upper limit branching fractions from this analysis. |
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Figure 4-b:
The four-muon invariant mass distribution for $\Upsilon(\text{1S})\Upsilon(\text{1S})$ candidates (error bars for empty bins are not shown). The result of the maximum likelihood fit to background (Bkg) is superimposed (solid blue line). For illustrative purposes, the plot shows the distributions for simulated Higgs and Z boson signals (dashed and dashed-dotted red lines) normalized to their observed 95% CL upper limit branching fractions from this analysis. |
| Tables | |
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Table 1:
Exclusion limits at 95% CL on the branching fractions of the H and Z boson decays. The second column lists the observed limits for the case that both intermediate particles are longitudinally polarized ($\lambda _\theta = -$1) as described in the text. The third column shows the median expected limits with the upper and lower bounds in the expected 68% CL intervals. The last two columns list observed upper limits for unpolarized ($\lambda _\theta = $ 0) and transversely polarized ($\lambda _\theta = +$1) intermediate particles. |
| Summary |
| This Letter presents the first search for decays of the Higgs boson (H) into a Z boson and a J/$\psi$ meson in four-lepton final states. Data from proton-proton collisions at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of about 138 fb$^{-1}$, are used. Using the same data, decays of the Higgs and Z boson into quarkonium pairs are also searched for. No excess of a Higgs or Z boson signal above background is found in any of the searched channels and upper limits on branching fractions ($\mathcal{B}$) at the 95% confidence level for various polarization scenarios are set. The Higgs boson decay is also searched for in channels where, before decaying into muon pairs, one or both J/$\psi$ mesons could be the result of an inclusive $\psi(\text{2S})$ to J/$\psi$ transition, and the $\Upsilon(\text{nS}) (\mathrm{n}=1,2)$ mesons could be the result of inclusive transitions from $\Upsilon(\text{nS}) (\mathrm{n}=2,3)$ mesons. The observed upper limits for the Higgs and Z boson decays for longitudinally polarized mesons are $\mathcal{B}(\mathrm{H}\to\mathrm{Z}\mathrm{J}/\psi) < $ 1.9 $\times$ 10$^{-3}$, $\mathcal{B}(\mathrm{H}\to\mathrm{Z}\psi(\text{2S})) < $ 6.6 $\times$ 10$^{-3}$, $\mathcal{B}(\mathrm{H}\to\mathrm{J}/\psi\mathrm{J}/\psi) < $ 3.8 $\times$ 10$^{-4}$, $\mathcal{B}(\mathrm{H}\to\psi(\text{2S})\mathrm{J}/\psi) < $ 2.1 $\times$ 10$^{-3}$, $\mathcal{B}(\mathrm{H}\to\psi(\text{2S})\psi(\text{2S})) < $ 3.0 $\times$ 10$^{-3}$, $\mathcal{B}(\mathrm{H}\to\Upsilon(\text{nS})\Upsilon(\text{mS})) < $ 3.5 $\times$ 10$^{-4}$, $\mathcal{B}(\mathrm{H}\to\Upsilon(\text{1S})\Upsilon(\text{1S})) < $ 1.7 $\times$ 10$^{-3}$, $\mathcal{B}(\mathrm{Z}\to\mathrm{J}/\psi\mathrm{J}/\psi) < $ 11 $\times$ 10$^{-7}$, $\mathcal{B}(\mathrm{Z}\to\Upsilon(\text{nS})\Upsilon(\text{mS})) < $ 3.9 $\times$ 10$^{-7}$, and $\mathcal{B}(\mathrm{Z}\to\Upsilon(\text{1S})\Upsilon(\text{1S})) < $ 1.8 $\times$ 10$^{-6}$. The observed upper limit branching fraction for $\mathrm{H}\to\mathrm{Z}\mathrm{J}/\psi$ is about 800 times the value predicted by the standard model [17,18,19]. For $\mathrm{H}\to\Upsilon(\text{nS})\Upsilon(\text{mS})$ the upper limit is about one order of magnitude higher than predicted by earlier standard model calculations [23]. |
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