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| CMS-SMP-17-012 ; CERN-EP-2018-250 | ||
| Search for rare decays of Z and Higgs bosons to $\mathrm{J}/\psi$ and a photon in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 23 October 2018 | ||
| Eur. Phys. J. C 79 (2019) 94 | ||
| Abstract: A search is presented for decays of Z and Higgs bosons to a $\mathrm{J}/\psi$ meson and a photon, with the subsequent decay of the $\mathrm{J}/\psi$ to $\mu^{+}\mu^{-}$. The analysis uses data from proton-proton collisions with an integrated luminosity of 35.9 fb$^{-1}$ at $\sqrt{s} = $ 13 TeV collected with the CMS detector at the LHC. The observed limit on the $\mathrm{Z}\to\mathrm{J}/\psi\gamma$ decay branching fraction, assuming that the $\mathrm{J}/\psi$ meson is produced unpolarized, is $ 1.4\times10^{-6} $ at 95% confidence level, which corresponds to a rate higher than expected in the standard model by a factor of 15. For extreme-polarization scenarios, the observed limit changes from -13.6 to +8.6% with respect to the unpolarized scenario. The observed upper limit on the branching fraction for $\mathrm{H}\to\mathrm{J}/\psi\gamma$ where the $\mathrm{J}/\psi$ meson is assumed to be transversely polarized is $ 7.6\times 10^{-4} $, a factor of 260 larger than the standard model prediction. The results for the Higgs boson are combined with previous data from proton-proton collisions at $\sqrt{s} = $ 8 TeV to produce an observed upper limit on the branching fraction for $\mathrm{H}\to\mathrm{J}/\psi\gamma$ that is a factor of 220 larger than the standard model value. | ||
| Links: e-print arXiv:1810.10056 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Feynman diagrams for Z (or H) $\to {{\mathrm {J}\psi}} \gamma $ decay. The left-most diagram shows the direct and the remaining diagrams the indirect processes. |
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Figure 1-a:
Feynman diagram for Z (or H) $\to {{\mathrm {J}\psi}} \gamma $ decay. The shows the direct process. |
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Figure 1-b:
Feynman diagram for Z (or H) $\to {{\mathrm {J}\psi}} \gamma $ decay. The shows an indirect process. |
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Figure 1-c:
Feynman diagram for Z (or H) $\to {{\mathrm {J}\psi}} \gamma $ decay. The shows an indirect process. |
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Figure 1-d:
Feynman diagram for Z (or H) $\to {{\mathrm {J}\psi}} \gamma $ decay. The shows an indirect process. |
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Figure 2:
Main Feynman diagrams for the Drell-Yan process in $ {\mathrm {p}} {\mathrm {p}}\to {\mathrm {Z}}\to \mu \mu \gamma $. The background exhibits a peak in $m_{\mu \mu \gamma}$ at the Z boson mass. |
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Figure 2-a:
Feynman diagram for the Drell-Yan process in $ {\mathrm {p}} {\mathrm {p}}\to {\mathrm {Z}}\to \mu \mu \gamma $. The background exhibits a peak in $m_{\mu \mu \gamma}$ at the Z boson mass. |
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Figure 2-b:
Feynman diagram for the Drell-Yan process in $ {\mathrm {p}} {\mathrm {p}}\to {\mathrm {Z}}\to \mu \mu \gamma $. The background exhibits a peak in $m_{\mu \mu \gamma}$ at the Z boson mass. |
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Figure 3:
Main Feynman diagrams for the Higgs boson Dalitz decay of $ {\mathrm {H}} \to \gamma ^{*}\gamma \to \mu \mu \gamma $. The background exhibits a peak in $m_{\mu \mu \gamma}$ at the Higgs boson mass. |
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Figure 3-a:
Feynman diagram for the Higgs boson Dalitz decay of $ {\mathrm {H}} \to \gamma ^{*}\gamma \to \mu \mu \gamma $. The background exhibits a peak in $m_{\mu \mu \gamma}$ at the Higgs boson mass. |
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Figure 3-b:
Feynman diagram for the Higgs boson Dalitz decay of $ {\mathrm {H}} \to \gamma ^{*}\gamma \to \mu \mu \gamma $. The background exhibits a peak in $m_{\mu \mu \gamma}$ at the Higgs boson mass. |
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Figure 3-c:
Feynman diagram for the Higgs boson Dalitz decay of $ {\mathrm {H}} \to \gamma ^{*}\gamma \to \mu \mu \gamma $. The background exhibits a peak in $m_{\mu \mu \gamma}$ at the Higgs boson mass. |
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Figure 4:
The $m_{\mu \mu}$ distributions in the Z (left) and Higgs (right) boson searches. The number of events in the distributions from signal events is set to respective factors of 40 and 750 larger than the SM values for the predicted yields for Z and H boson decays. The number of events in distributions in the resonant background samples is normalized to 5 and 150 multiples in the expected yields. |
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Figure 4-a:
The $m_{\mu \mu}$ distribution in the Z boson search. The number of events in the distribution from signal events is set to a factor of 40 larger than the SM value for the predicted yield for the Z boson decay. The number of events in the distribution in the resonant background sample is normalized to 5 times the expected yield. |
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Figure 4-b:
The $m_{\mu \mu}$ distribution in the Higgs boson search. The number of events in the distribution from signal events is set to a factor of 750 larger than the SM value for the predicted yield for the H boson decay. The number of events in the distribution in the resonant background sample is normalized to 150 times the expected yield. |
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Figure 5:
The photon $ {E_{\mathrm {T}}} $ distributions in the Z (left) and Higgs (right) boson searches. The number of events in the distributions from signal events is set to factors of 40 and 750 those of the SM predicted yields for the Z and H boson decays, respectively. The number of events in distributions in the resonant background samples are normalized to respective factors of 5 and 150 larger than the expected yields. |
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Figure 5-a:
The photon $ {E_{\mathrm {T}}} $ distribution in the Z boson search. The number of events in the distribution from signal events is set to a factor of 40 that of the SM predicted yield for the Z H boson decay. The number of events in the distribution in the resonant background sample is normalized to a factor of 5 larger than the expected yield. |
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Figure 5-b:
The photon $ {E_{\mathrm {T}}} $ distribution in the Higgs boson search. The number of events in the distribution from signal events is set to a factor of 750 that of the SM predicted yield for the Z H boson decay. The number of events in the distribution in the resonant background sample is normalized to a factor of 150 larger than the expected yield. |
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Figure 6:
The proper decay time, t, distributions in the Z (left) and Higgs (right) boson searches. Distributions in simulated events are normalized to the number of selected events in data. The distributions suggest that the $ {{\mathrm {J}\psi}} $ candidates reconstructed in data, just as signal events, are produced promptly at the pp interaction point, and not from displaced heavy-hadron decays. |
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Figure 6-a:
The proper decay time, t, distribution in the Z boson search. The distribution in simulated events is normalized to the number of selected events in data. The distribution suggests that the $ {{\mathrm {J}\psi}} $ candidates reconstructed in data, just as signal events, are produced promptly at the pp interaction point, and not from displaced heavy-hadron decays. |
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Figure 6-b:
The proper decay time, t, distribution in the Higgs boson search. The distribution in simulated events is normalized to the number of selected events in data. The distribution suggests that the $ {{\mathrm {J}\psi}} $ candidates reconstructed in data, just as signal events, are produced promptly at the pp interaction point, and not from displaced heavy-hadron decays. |
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Figure 7:
Fits to nonresonant background using lowest-order unbiased functions to describe the three-body invariant mass $ m_{\mu \mu \gamma} $ distributions observed in data for the $\mathrm{Z} \to {{\mathrm {J}\psi}} \gamma $ channel in the EB high R9 category (top left), the EB low R9 category (top right), the EE category (bottom left), as well as the $\mathrm{H} \to {{\mathrm {J}\psi}} \gamma $ channel (bottom right). |
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Figure 7-a:
Fit to nonresonant background using a lowest-order unbiased function to describe the three-body invariant mass $ m_{\mu \mu \gamma} $ distribution observed in data for the $\mathrm{Z} \to {{\mathrm {J}\psi}} \gamma $ channel in the EB high R9 category. |
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Figure 7-b:
Fit to nonresonant background using a lowest-order unbiased function to describe the three-body invariant mass $ m_{\mu \mu \gamma} $ distribution observed in data for the $\mathrm{Z} \to {{\mathrm {J}\psi}} \gamma $ channel in the EB low R9 category. |
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Figure 7-c:
Fit to nonresonant background using a lowest-order unbiased function to describe the three-body invariant mass $ m_{\mu \mu \gamma} $ distribution observed in data for the $\mathrm{Z} \to {{\mathrm {J}\psi}} \gamma $ channel in the EE category. |
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Figure 7-d:
Fit to nonresonant background using a lowest-order unbiased function to describe the three-body invariant mass $ m_{\mu \mu \gamma} $ distribution observed in data for the $\mathrm{H} \to {{\mathrm {J}\psi}} \gamma $ channel. |
| Tables | |
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Table 1:
The number of observed Z or H boson events, the expected signal yields, the expected nonresonant background with uncertainties estimated from the fit (described in Section 5), and the expected resonant background (see Section 3) contribution in the ranges of 81 or 120 $ < m_{\mu \mu \gamma} < $ 101 or 130 GeV, respectively, for the Z or H boson searches. |
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Table 2:
Systematic uncertainties in both the searches for $ {\mathrm {Z}}\to {{\mathrm {J}\psi}} \gamma $ and $ {\mathrm {H}} \to {{\mathrm {J}\psi}} \gamma $. In the $ {\mathrm {Z}}\to {{\mathrm {J}\psi}} \gamma $ search, the uncertainties are averaged over all categories. |
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Table 3:
Observed and expected limits (the latter in parentheses) on the $\sigma ({\mathrm {p}} {\mathrm {p}}\to {\mathrm {Z}}\ ({\mathrm {H}})\to ({{\mathrm {J}\psi}} \to \mu \mu)\gamma)\ (\text {fb})$ cross sections and branching fractions of $ {\mathrm {Z}}\ ({\mathrm {H}})\to {{\mathrm {J}\psi}} \gamma $ decay, with the latter computed assuming the SM cross sections of the $ {\mathrm {Z}}\ ({\mathrm {H}})$ boson. Dependence of the branching fractions in Z decay for fully transverse and longitudinal polarizations for $ {{\mathrm {J}\psi}} $. The upper and lower bounds of the expected 68% CL intervals for the limits are shown respectively as superscripts and subscripts. |
| Summary |
| A search is performed for decays of the standard model (SM) Z and Higgs bosons into a $\mathrm{J}/\psi$ meson and a photon, with the $\mathrm{J}/\psi$ meson subsequently decaying into $\mu^{+}\mu^{-}$. The data are from ${\mathrm{p}}{\mathrm{p}}$ collisions at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. No excess is observed above the measured background. The observed and expected exclusion limits at 95% confidence level (CL) on the branching fraction of the Z boson decay in the unpolarized case are $\mathcal{B}(\mathrm{Z}\to\mathrm{J}/\psi\gamma) < $ 1.4 and $1.6^{+0.7}_{-0.5}\, 10^{-6}$, corresponding to factors of 15 and 18 greater than the SM prediction. The 68% CL range in the confidence interval is shown as the subscript and superscript. Extreme polarization possibilities give rise to changes from -13.6 and -13.5% for a longitudinally polarized $\mathrm{J}/\psi$ meson, to +8.6 and +8.2%, for a transversely polarized $\mathrm{J}/\psi$ meson, in the respective observed and expected branching fractions. The 95% CL limit on the branching fraction of the Higgs boson are $\mathcal{B}(\mathrm{H}\to\mathrm{J}/\psi\gamma) < 7.6 $ and $5.2^{+2.4}_{-1.6}\,10^{-4}$, corresponding to factors of 260 and 170 times the SM value. The results for the Higgs boson channel are combined with previous CMS data from proton-proton collisions at $\sqrt{s} = $ 8 TeV to produce observed and expected upper limits on the branching fraction for the decay $\mathrm{H}\to\mathrm{J}/\psi\gamma$ of factors of 220 and 160 larger than the SM predictions. |
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