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| CMS-PAS-HIG-20-008 | ||
| Search for Higgs boson decays into Z and J/$\psi$ and for Higgs and Z boson decays into J/$\psi$ or $\Upsilon$ pairs at CMS | ||
| CMS Collaboration | ||
| January 2022 | ||
| Abstract: For the first time, decays of the Higgs boson into a Z boson and a J/$\psi$ meson are searched for in four-lepton final states with the CMS detector at the LHC. A proton-proton collision data set corresponding to an integrated luminosity of 138 fb$^{-1}$ is exploited. In addition, Higgs decays into pairs of J/$\psi$ or $\Upsilon$ mesons are studied in the same data. Events with Z boson decays into an electron or muon pair, or with quarkonium resonances decaying into muon pairs, are selected. An observation of such decays with this sample would indicate the presence of physics beyond the standard model, and no significant excess is observed. Upper limits at the 95% confidence level are placed on the branching fractions of these decays. Higgs decay branching fractions for $\mathrm{H}\to \mathrm{Z}\, \psi\text{(2S)}$, $\mathrm{H}\to \mathrm{J/}\psi\, \psi\text{(2S)}$, and $\mathrm{H}\to \psi\text{(2S)}\, \psi \text{(2S)}$ are obtained via the inclusive decay of $\psi\text{(2S)}$ into J/$\psi$. Furthermore, upper limits on the branching fraction for the Higgs boson decay into $\Upsilon\mathrm{(1S)}$ and $\Upsilon\mathrm{(nS)}$ ($n =$ 1, 2, 3) pairs are found, where for the latter all pairings of the $\Upsilon\mathrm{(1S)}$, $\Upsilon\mathrm{(2S)}$, and $\Upsilon\mathrm{(3S)}$ resonances decaying into muon pairs and the feed-down decays into lower $\Upsilon$ states are included. The decay of the Z boson into J/$\psi$ or $\Upsilon$ pairs is also searched for. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to PLB. The superseded preliminary plots can be found here. |
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| 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 resonance. 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 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 resonance. The diagrams represent Higgs boson decays into quarkonium pairs when replacing the bottom section with the upper half in each. |
png pdf |
Figure 1-b:
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 resonance. 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-c:
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 resonance. 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 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 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 green line) signals normalized to their observed upper limit branching fractions at 95% CL as obtained in this analysis, where $\psi \text {(2S)}$ decays into J/$\psi$. |
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Figure 2-a:
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 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 green line) signals normalized to their observed upper limit branching fractions at 95% CL as obtained in this analysis, where $\psi \text {(2S)}$ decays into J/$\psi$. |
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Figure 2-b:
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 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 green line) signals normalized to their observed upper limit branching fractions at 95% CL as obtained in this analysis, where $\psi \text {(2S)}$ decays into J/$\psi$. |
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Figure 3:
The four-muon invariant mass distribution of J/$\psi$ 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 plots show the distributions for simulated signals of the Higgs and Z boson decaying into J/$\psi$ 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 green line) and $\mathrm{H} \to \psi \text {(2S)}\psi \text {(2S)}$ (dashed-dotted black line) are also shown, where $\psi \text {(2S)}$ decays into 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 $\rm {\Upsilon (nS) \Upsilon (mS)}$ (right) and $\rm {\Upsilon (1S) \Upsilon (1S)}$ 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 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 distributions for $\rm {\Upsilon (nS) \Upsilon (mS)}$ (right) and $\rm {\Upsilon (1S) \Upsilon (1S)}$ 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 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. |
png pdf |
Figure 4-b:
The four-muon invariant mass distributions for $\rm {\Upsilon (nS) \Upsilon (mS)}$ (right) and $\rm {\Upsilon (1S) \Upsilon (1S)}$ 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 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. |
| Tables | |
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Table 1:
Relative changes (in percent) of the acceptance for different extreme polarization scenarios with respect to the case where both decay products are longitudinally polarized. In the other scenarios, both decay products are assumed to be either unpolarized or transversely polarized. |
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Table 2:
Exclusion limits at 95% CL for the branching fractions of the H and Z boson decays. 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. The last two columns list observed upper limits for different polarization assumptions as described in the text. |
| Summary |
| In summary, this note presents the first search for decays of the Higgs boson into a Z boson and J/$\psi$ meson in four-lepton final states. Furthermore, results on upper limits of branching fractions for Higgs decays into pairs of J/$\psi$ or $\rm{\Upsilon (1S)}$ or $\rm{\Upsilon (nS) (n=1,2,3)} $ mesons in the four-muon final state are obtained. Data from pp collisions at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of about 138 fb$^{-1}$, are used. No excess of a Higgs (Z) boson signal above background is found in any of the searched channels. The observed upper limits at 95% confidence level on the branching fractions for the Higgs boson decays for longitudinally polarized mesons are $\rm{\mathcal{B}(\mathrm{H} \to \mathrm{Z} \mathrm{J}/\psi) < 1.9\times 10^{-3}}$, $\rm{\mathcal{B}(\mathrm{H} \to \mathrm{J}/\psi \mathrm{J}/\psi) < 3.8\times 10^{-4}}$, $\rm{\mathcal{B}(\mathrm{H} \to \Upsilon(nS) \Upsilon(mS)) < 3.5\times 10^{-4}}$ and $\mathcal{B}(\mathrm{H} \to \Upsilon\text{(1S)} \Upsilon\text{(1S)}) < 1.7\times 10^{-3}$. The expected upper limits on the branching fractions for the Z boson decay in the longitudinally polarized scenario are $\mathcal{B}(\mathrm{Z} \to \mathrm{J}/\psi \mathrm{J}/\psi) < 10.8\times 10^{-7}$, $\mathcal{B}(\mathrm{Z} \to \Upsilon\text{(nS)} \Upsilon\text{(mS)}) < 3.9\times 10^{-7}$, and $\mathcal{B}(\mathrm{Z} \to \Upsilon\text{(1S)} \Upsilon\text{(1S)}) < 1.8\times 10^{-6}$. The Higgs boson decay is also searched for in channels where one or both J/$\psi$ mesons could be the result of an inclusive $\psi \text{(2S)}$ to J/$\psi$ transition. The expected upper limits at 95% confidence level on the branching fractions for the Higgs boson decays for these feed-down channels are also listed in Tab. xxxxx. Extreme polarization scenarios give rise to variations in the observed Higgs boson decay branching fractions between $+$17.5 and 20.4% ($+$24.1 and 30.2%) for uniformly (fully transversely) polarized intermediate particles with respect to the case where both decay particles are longitudinally polarized. |
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Compact Muon Solenoid LHC, CERN |
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