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| CMS-PAS-SMP-17-012 | ||
| Search for the rare decays of Z bosons and Higgs bosons to $\mathrm{J/}\psi$ plus photon at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| June 2018 | ||
| Abstract: A search for decays of Z and Higgs bosons to $\mathrm{J/}\psi$ and a photon, with the subsequent decay of the $\mathrm{J/}\psi$ to $\mu^{+}\mu^{-}$, in proton-proton (pp) collisions at a center-of-mass energy ($\sqrt{s}$) of 13 TeV, is presented. The analysis uses a data sample corresponding to an integrated luminosity of 35.9 fb$^{-1}$ collected with the CMS detector at the LHC in 2016. The observed (expected) upper limit on the $\mathrm{Z}\to\mathrm{J/}\psi\ \gamma$ decay branching fraction, assuming that the $\mathrm{J/}\psi$ is unpolarized, is $ 1.4\ (1.6) \times 10^{-6}$ at 95% confidence level, which corresponds to 15 (18) times the standard model (SM) prediction. For the extreme polarization scenarios the observed (expected) limit varies from $ - 13.6 $ ($ - 13.5 $) to $ +8.6 $ ($ +8.2 $)%. The observed (expected) upper limit on the branching fraction for $\mathrm{H}\to\mathrm{J/}\psi\ \gamma$ with $m_{\mathrm{H}} = $ 125 GeV is $ 7.6\ (5.2)\times 10^{-4} $, 260 (170) times the SM prediction, at 95% confidence level. The $\mathrm{J/}\psi$ from the Higgs decay is assumed to be completely transversely polarized. The results for the Higgs boson decay are combined with the results from pp collisions at $\sqrt{s}= $ 8 TeV corresponding to 19.7 fb$^{-1}$ and this results in an expected (observed) upper limit on the branching fraction for $\mathrm{H}\to\mathrm{J/}\psi\ \gamma$ of 220 (160) times the SM prediction. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, EPJC 79 (2019)94. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Feynman diagrams for $ {\mathrm {Z}}({\mathrm {H}})\to {{\mathrm {J}/\psi}} \gamma $. The diagram on the left shows the direct process and the remaining diagrams are the indirect processes. |
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Figure 1-a:
Feynman diagrams for $ {\mathrm {Z}}({\mathrm {H}})\to {{\mathrm {J}/\psi}} \gamma $. The diagram on the left shows the direct process and the remaining diagrams are the indirect processes. |
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Figure 1-b:
Feynman diagrams for $ {\mathrm {Z}}({\mathrm {H}})\to {{\mathrm {J}/\psi}} \gamma $. The diagram on the left shows the direct process and the remaining diagrams are the indirect processes. |
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Figure 1-c:
Feynman diagrams for $ {\mathrm {Z}}({\mathrm {H}})\to {{\mathrm {J}/\psi}} \gamma $. The diagram on the left shows the direct process and the remaining diagrams are the indirect processes. |
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Figure 1-d:
Feynman diagrams for $ {\mathrm {Z}}({\mathrm {H}})\to {{\mathrm {J}/\psi}} \gamma $. The diagram on the left shows the direct process and the remaining diagrams are the indirect processes. |
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Figure 2:
Main diagrams for the Drell-Yan process, $ {\mathrm {p}} {\mathrm {p}}\to {\mathrm {Z}}\to \mu \mu \gamma $, which is the background that will exhibit a peak in $m_{\mu \mu \gamma}$ at the Z boson mass, $m_{{\mathrm {Z}}}$. |
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Figure 2-a:
Main diagrams for the Drell-Yan process, $ {\mathrm {p}} {\mathrm {p}}\to {\mathrm {Z}}\to \mu \mu \gamma $, which is the background that will exhibit a peak in $m_{\mu \mu \gamma}$ at the Z boson mass, $m_{{\mathrm {Z}}}$. |
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Figure 2-b:
Main diagrams for the Drell-Yan process, $ {\mathrm {p}} {\mathrm {p}}\to {\mathrm {Z}}\to \mu \mu \gamma $, which is the background that will exhibit a peak in $m_{\mu \mu \gamma}$ at the Z boson mass, $m_{{\mathrm {Z}}}$. |
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Figure 3:
Main diagrams for the Higgs Dalitz decay, $ {\mathrm {H}} \to \gamma ^{*}\gamma \to \mu \mu \gamma $, which is the background that will exhibit a peak in $m_{\mu \mu \gamma}$ at the Higgs mass, $m_{{\mathrm {H}}}$. |
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Figure 3-a:
Main diagrams for the Higgs Dalitz decay, $ {\mathrm {H}} \to \gamma ^{*}\gamma \to \mu \mu \gamma $, which is the background that will exhibit a peak in $m_{\mu \mu \gamma}$ at the Higgs mass, $m_{{\mathrm {H}}}$. |
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Figure 3-b:
Main diagrams for the Higgs Dalitz decay, $ {\mathrm {H}} \to \gamma ^{*}\gamma \to \mu \mu \gamma $, which is the background that will exhibit a peak in $m_{\mu \mu \gamma}$ at the Higgs mass, $m_{{\mathrm {H}}}$. |
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Figure 3-c:
Main diagrams for the Higgs Dalitz decay, $ {\mathrm {H}} \to \gamma ^{*}\gamma \to \mu \mu \gamma $, which is the background that will exhibit a peak in $m_{\mu \mu \gamma}$ at the Higgs mass, $m_{{\mathrm {H}}}$. |
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Figure 4:
The $m_{\mu \mu}$ distributions in the Z (left) and Higgs (right) boson searches. |
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Figure 4-a:
The $m_{\mu \mu}$ distributions in the Z (left) and Higgs (right) boson searches. |
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Figure 4-b:
The $m_{\mu \mu}$ distributions in the Z (left) and Higgs (right) boson searches. |
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Figure 5:
The proper decay time, t, distributions in the Z (left) and Higgs (right) boson searches. |
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Figure 5-a:
The proper decay time, t, distributions in the Z (left) and Higgs (right) boson searches. |
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Figure 5-b:
The proper decay time, t, distributions in the Z (left) and Higgs (right) boson searches. |
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Figure 6:
Background fits with the lowest order unbiased functions to the three-body invariant mass $m_{\mu\mu\gamma}$ distributions in data for ${\mathrm {Z}} \to {{\mathrm {J}/\psi}} \gamma$ in EB-HighR9 category (top), EB-LowR9 category (middle left), EE category (middle right), and ${\mathrm {H}}\to {{\mathrm {J}/\psi}}\gamma$ (bottom). |
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Figure 6-a:
Background fits with the lowest order unbiased functions to the three-body invariant mass $m_{\mu\mu\gamma}$ distributions in data for ${\mathrm {Z}} \to {{\mathrm {J}/\psi}} \gamma$ in EB-HighR9 category (top), EB-LowR9 category (middle left), EE category (middle right), and ${\mathrm {H}}\to {{\mathrm {J}/\psi}}\gamma$ (bottom). |
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Figure 6-b:
Background fits with the lowest order unbiased functions to the three-body invariant mass $m_{\mu\mu\gamma}$ distributions in data for ${\mathrm {Z}} \to {{\mathrm {J}/\psi}} \gamma$ in EB-HighR9 category (top), EB-LowR9 category (middle left), EE category (middle right), and ${\mathrm {H}}\to {{\mathrm {J}/\psi}}\gamma$ (bottom). |
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Figure 6-c:
Background fits with the lowest order unbiased functions to the three-body invariant mass $m_{\mu\mu\gamma}$ distributions in data for ${\mathrm {Z}} \to {{\mathrm {J}/\psi}} \gamma$ in EB-HighR9 category (top), EB-LowR9 category (middle left), EE category (middle right), and ${\mathrm {H}}\to {{\mathrm {J}/\psi}}\gamma$ (bottom). |
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Figure 6-d:
Background fits with the lowest order unbiased functions to the three-body invariant mass $m_{\mu\mu\gamma}$ distributions in data for ${\mathrm {Z}} \to {{\mathrm {J}/\psi}} \gamma$ in EB-HighR9 category (top), EB-LowR9 category (middle left), EE category (middle right), and ${\mathrm {H}}\to {{\mathrm {J}/\psi}}\gamma$ (bottom). |
| Tables | |
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Table 1:
The number of selected events in data, the expected signal yield, and the expected peaking background contribution for the integrated luminosity of 35.9 fb$^{-1}$. The selected events are required to have 70 (100) $ < m_{\mu \mu \gamma} < $ 120 (150) GeV for the Z (H) boson search. |
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Table 2:
Summary of the impacts of different polarization scenarios on the expected yield for the Z boson decay. |
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Table 3:
Systematic uncertainties in both Higgs and Z boson decays. In the Z boson decay, the pre-fit values, which are uncertainties before profiling in the limit setting procedure, are averaged over all categories. |
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Table 4:
Upper observed (expected) limits on branching fraction of $ {\mathrm {Z}} \to {{\mathrm {J}/\psi}} \gamma $ and $ {\mathrm {H}} \to {{\mathrm {J}/\psi}} \gamma $ decays. |
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Table 5:
Variations of the branching fractions of the Z decay for complete transverse and longitudinal polarizations for $ {{\mathrm {J}/\psi}} $, and the differences (labeled as $\Delta $ in the table) with respect to the unpolarized value. |
| Summary |
| A search is performed for the decays of the SM Z and Higgs bosons into a $\mathrm{J}/\psi$ and a photon with $\mathrm{J}/\psi$ subsequently decaying into $\mu^{+}\mu^{-}$. No excess has been observed above the predicted background. The observed (expected) exclusion limit at 95% confidence level on the branching ratio of the Z boson decay in the unpolarized scenario is set at $\mathcal{B}(\mathrm{Z}\to\mathrm{J}/\psi\ \gamma) < 1.4\ (1.6^{+0.6}_{-0.5})\times 10^{-6}$, corresponding to 15 (17) times its SM prediction. Extreme polarization scenarios give rise to variations from -13.6 (-13.5)%, for a fully longitudinally polarized $\mathrm{J}/\psi$, to +8.6 (+8.2)%, for a fully transversely polarized $\mathrm{J}/\psi$, on the observed (expected) branching ratio. The limit on the branching ratio of the Higgs boson is set at $\mathcal{B}(\mathrm{H}\to\mathrm{J}/\psi\ \gamma) < 7.6\ (5.2^{+2.4}_{-1.6})\times 10^{-4}$, corresponding to 260 (170) times the SM value. The results for the Higgs boson decay are combined with the results from pp collisions at $\sqrt{s} = $ 8 TeV corresponding to 19.7 fb$^{-1}$ and this results in an expected (observed) upper limit on the branching ratio for $\mathrm{H}\to\mathrm{J}/\psi\ \gamma$ of 220 (160) times the SM prediction. The current sensitivity of the $\mathrm{H}\to\mathrm{J}/\psi\ \gamma$ search is compatible to the $\mathrm{H}\to\mathrm{c\bar{c}}$ search from the ATLAS Collaboration. More data is needed to approach the SM prediction. |
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