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| CMS-PAS-SMP-22-012 | ||
| Search for the rare decays of the Z and Higgs bosons to a $ \mathrm{J}/\psi $ or $ \psi^{\prime} $ meson and a photon in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 30 November 2023 | ||
| Abstract: A search is performed for the rare decays of the Z and Higgs bosons to a photon and a charmed meson $ \mathrm{J}/\psi $ or $ \psi^{\prime} $, which subsequentially decays to a pair of muons. The data set corresponds to an integrated luminosity of 123 fb$ ^{-1} $ of proton-proton collisions at $ \sqrt{s}= $ 13 TeV collected with the CMS detector at the LHC. The presence of two resonances in the signal is used to discriminate and estimate the non-resonant backgrounds. No evidence for branching fractions to these rare decay channels larger than predicted in the standard model is observed. Upper limits at 95% confidence level are set on $ \mathcal{B}(\mathrm{H}\to\mathrm{J}/\psi\gamma) < 2.6 \times 10^{-4} $, $ \mathcal{B}(\mathrm{H}\to\psi^{\prime}\gamma) < 9.9 \times 10^{-4} $, $ \mathcal{B}(\mathrm{Z}\to\mathrm{J}/\psi\gamma) < 0.6 \times 10^{-6} $ and $ \mathcal{B}(\mathrm{Z}\to\psi^{\prime}\gamma) < 1.3 \times 10^{-6} $. The ratio of the Higgs boson coupling modifiers $ \kappa_{c}/\kappa_{\gamma} $ is constrained to be in the interval $ (-157,+199) $ at 95% confidence level. When assuming $ \kappa_{\gamma}= $ 1, the observed interval becomes $ (-166,+208) $. | ||
| Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Leading-order Feynman diagrams of Z and Higgs boson rare decays to $ \psi $ (1S) or $ \psi $ (2S), and a photon, through the direct process (top left) and the indirect processes (top right, bottom left, and bottom right). |
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Figure 1-a:
Leading-order Feynman diagrams of Z and Higgs boson rare decays to $ \psi $ (1S) or $ \psi $ (2S), and a photon, through the direct process (top left) and the indirect processes (top right, bottom left, and bottom right). |
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Figure 1-b:
Leading-order Feynman diagrams of Z and Higgs boson rare decays to $ \psi $ (1S) or $ \psi $ (2S), and a photon, through the direct process (top left) and the indirect processes (top right, bottom left, and bottom right). |
png pdf |
Figure 1-c:
Leading-order Feynman diagrams of Z and Higgs boson rare decays to $ \psi $ (1S) or $ \psi $ (2S), and a photon, through the direct process (top left) and the indirect processes (top right, bottom left, and bottom right). |
png pdf |
Figure 1-d:
Leading-order Feynman diagrams of Z and Higgs boson rare decays to $ \psi $ (1S) or $ \psi $ (2S), and a photon, through the direct process (top left) and the indirect processes (top right, bottom left, and bottom right). |
png pdf |
Figure 2:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF HP category. Top right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF LP category. Bottom left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ VBF category. Bottom right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ HF category. |
png pdf |
Figure 2-a:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF HP category. Top right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF LP category. Bottom left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ VBF category. Bottom right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ HF category. |
png pdf |
Figure 2-b:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF HP category. Top right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF LP category. Bottom left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ VBF category. Bottom right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ HF category. |
png pdf |
Figure 2-c:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF HP category. Top right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF LP category. Bottom left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ VBF category. Bottom right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ HF category. |
png pdf |
Figure 2-d:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF HP category. Top right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ ggF LP category. Bottom left: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ VBF category. Bottom right: $ \mathrm{H}\to\psi $ (1S) $ \gamma $ HF category. |
png pdf |
Figure 3:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ HP category. Top right: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ LP category. Bottom left: $ \mathrm{H}\to\psi $ (2S) $ \gamma $ category. Bottom right: $ \mathrm{Z}\to\psi $ (2S) $ \gamma $ category. |
png pdf |
Figure 3-a:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ HP category. Top right: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ LP category. Bottom left: $ \mathrm{H}\to\psi $ (2S) $ \gamma $ category. Bottom right: $ \mathrm{Z}\to\psi $ (2S) $ \gamma $ category. |
png pdf |
Figure 3-b:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ HP category. Top right: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ LP category. Bottom left: $ \mathrm{H}\to\psi $ (2S) $ \gamma $ category. Bottom right: $ \mathrm{Z}\to\psi $ (2S) $ \gamma $ category. |
png pdf |
Figure 3-c:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ HP category. Top right: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ LP category. Bottom left: $ \mathrm{H}\to\psi $ (2S) $ \gamma $ category. Bottom right: $ \mathrm{Z}\to\psi $ (2S) $ \gamma $ category. |
png pdf |
Figure 3-d:
Background-only fit using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test, and ranked according to the fit $ \chi^2 $. The resonant background contributions are added with normalization fixed to the SM expectation. Top left: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ HP category. Top right: $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ LP category. Bottom left: $ \mathrm{H}\to\psi $ (2S) $ \gamma $ category. Bottom right: $ \mathrm{Z}\to\psi $ (2S) $ \gamma $ category. |
png pdf |
Figure 4:
Results of the main background fit in the CR, using the power-law, exponential, and Bernstein polynomial functions with the optimal number of parameters determined with the F-test. |
png pdf |
Figure 5:
Observed and expected (with $ {\pm}1,\,{\pm} $ 2 standard deviation bands) exclusion limits on the branching fraction of the $ (\mathrm{H},\mathrm{Z}) \to \psi $ (nS) $ \gamma $ processes. |
| Tables | |
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Table 1:
SM predictions of the branching fractions of the Higgs and Z bosons to $ \psi $ (nS) $ \gamma $, and measured branching fractions for the $ \psi $ (nS) $ \to\mu\mu $ decays [12]. |
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Table 2:
Sources of systematic uncertainties described in Section 6 and their impact on the signal strength. |
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Table 3:
Observed (expected) upper limits at 95% CL on the product of the cross section and the branching fraction of the $ (\mathrm{H},\mathrm{Z}) \to \psi $ (nS) $ \gamma $ processes. The normalized values with respect to the SM expectation are included as well and denoted as the signal strength parameter $ \mu $. The results are compared with previous ones [13,15]. |
| Summary |
| A search for the rare decays of the Z and H bosons to a photon and a $ \psi $ (nS) meson decaying to a pair of muons is presented. No statistically-significant excess has been observed over the standard model expectations. The data were collected by the CMS experiment at $ \sqrt{s}= $ 13 TeV during 2016--2018 and correspond to an integrated luminosity of 123 fb$ ^{-1} $. The upper limits on the branching fraction are set to 0.6 and 1.3 $ \times 10^{-6} $ for the $ \mathrm{Z}\to\psi $ (1S) $ \gamma $ and $ \mathrm{Z}\to\psi $ (2S) $ \gamma $ decays, and 2.6 and 9.9 $ \times 10^{-4} $ for the $ \mathrm{H}\to\psi $ (1S) $ \gamma $ and $ \mathrm{H}\to\psi $ (2S) $ \gamma $ decays, respectively. The limit for $ \mathrm{H}\to\psi $ (1S) $ \gamma $ translates to an interval constraint on the $ \kappa_{c}/\kappa_{\gamma} $ ratio of the Higgs boson coupling modifiers of $ (-157, +199) $; if the SM value of $ \kappa_{\gamma}= $ 1 is assumed, the observed interval is $ (-166,+208) $. |
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Compact Muon Solenoid LHC, CERN |
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