CMS-PAS-SMP-17-012

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.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, EPJC 79 (2019)94. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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, $m_{{\mathrm {Z}}}$ .
png pdf	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, $m_{{\mathrm {Z}}}$ .
png pdf	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, $m_{{\mathrm {Z}}}$ .
png pdf	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, $m_{{\mathrm {H}}}$ .
png pdf	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, $m_{{\mathrm {H}}}$ .
png pdf	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, $m_{{\mathrm {H}}}$ .
png pdf	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, $m_{{\mathrm {H}}}$ .
png pdf	Figure 4: The $m_{\mu \mu}$ distributions in the Z (left) and Higgs (right) boson searches.
png pdf	Figure 4-a: The $m_{\mu \mu}$ distributions in the Z (left) and Higgs (right) boson searches.
png pdf	Figure 4-b: The $m_{\mu \mu}$ distributions in the Z (left) and Higgs (right) boson searches.
png pdf	Figure 5: The proper decay time, t, distributions in the Z (left) and Higgs (right) boson searches.
png pdf	Figure 5-a: The proper decay time, t, distributions in the Z (left) and Higgs (right) boson searches.
png pdf	Figure 5-b: The proper decay time, t, distributions in the Z (left) and Higgs (right) boson searches.
png pdf	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).
png pdf	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).
png pdf	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).
png pdf	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).
png pdf	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
png pdf	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.
png pdf	Table 2: Summary of the impacts of different polarization scenarios on the expected yield for the Z boson decay.
png pdf	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.
png pdf	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.
png pdf	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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