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| CMS-PAS-HIG-22-003 | ||
| Search for the exotic decay of the Higgs boson into a Z boson and a light pseudoscalar decaying into two photons in pp collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 25 March 2023 | ||
| Abstract: A search for the exotic decay of the Higgs boson to a Z boson and a light pseudoscalar particle, decaying, respectively, to two leptons and two photons, is presented. The search is based on proton-proton collision data at a center-of-mass energy of $ \sqrt{s}= $ 13 TeV, collected by the CMS detector and corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The analysis probes pseudoscalar masses ($ m_a $) between 1 and 30 GeV, leading to two pairs of well-isolated leptons and photons. No significant deviation from the standard model expectation is observed. Upper limits at 95% confidence level are set on the product of the Higgs boson production cross section and its branching to two leptons and two photons. The observed (expected) limits range from 17.8 (17.9) fb for $ m_{a} = $ 1 GeV to 4.7 (6.9) fb for $ m_{a} = $ 30 GeV. Limits on axion-like particle models are also reported. | ||
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Links:
CDS record (PDF) ;
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These preliminary results are superseded in this paper, Accepted by PLB. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Distributions of the four most discriminating variables used as input to the BDT: $ \frac{(m_{a}-m_{a,hyp})}{m_{\ell\ell\gamma\gamma}} $ (top-left), leading photon's $ \sigma_{i\eta i\eta} $ (top-right), subleading photon's $ \sigma_{i\eta i\eta} $ (bottom-left), and leading photon's R9 (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 1-a:
Distributions of the four most discriminating variables used as input to the BDT: $ \frac{(m_{a}-m_{a,hyp})}{m_{\ell\ell\gamma\gamma}} $ (top-left), leading photon's $ \sigma_{i\eta i\eta} $ (top-right), subleading photon's $ \sigma_{i\eta i\eta} $ (bottom-left), and leading photon's R9 (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 1-b:
Distributions of the four most discriminating variables used as input to the BDT: $ \frac{(m_{a}-m_{a,hyp})}{m_{\ell\ell\gamma\gamma}} $ (top-left), leading photon's $ \sigma_{i\eta i\eta} $ (top-right), subleading photon's $ \sigma_{i\eta i\eta} $ (bottom-left), and leading photon's R9 (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 1-c:
Distributions of the four most discriminating variables used as input to the BDT: $ \frac{(m_{a}-m_{a,hyp})}{m_{\ell\ell\gamma\gamma}} $ (top-left), leading photon's $ \sigma_{i\eta i\eta} $ (top-right), subleading photon's $ \sigma_{i\eta i\eta} $ (bottom-left), and leading photon's R9 (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 1-d:
Distributions of the four most discriminating variables used as input to the BDT: $ \frac{(m_{a}-m_{a,hyp})}{m_{\ell\ell\gamma\gamma}} $ (top-left), leading photon's $ \sigma_{i\eta i\eta} $ (top-right), subleading photon's $ \sigma_{i\eta i\eta} $ (bottom-left), and leading photon's R9 (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 2:
Distributions of the BDT output for $ m_{a} = $ 1 GeV (top-left), 10 GeV (top-right), 20 GeV (bottom-left), and 30 GeV (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 2-a:
Distributions of the BDT output for $ m_{a} = $ 1 GeV (top-left), 10 GeV (top-right), 20 GeV (bottom-left), and 30 GeV (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 2-b:
Distributions of the BDT output for $ m_{a} = $ 1 GeV (top-left), 10 GeV (top-right), 20 GeV (bottom-left), and 30 GeV (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 2-c:
Distributions of the BDT output for $ m_{a} = $ 1 GeV (top-left), 10 GeV (top-right), 20 GeV (bottom-left), and 30 GeV (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 2-d:
Distributions of the BDT output for $ m_{a} = $ 1 GeV (top-left), 10 GeV (top-right), 20 GeV (bottom-left), and 30 GeV (bottom-right). The events pass the selection criteria described in Section 5, while the signal is scaled with a cross-section of 0.1 fb, and the background sample is normalized to 138 fb$ ^{-1} $. The systematic uncertainties included in the shaded band are related to the photon efficiency, lepton efficiency, and pile-up reweighting. |
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Figure 3:
Fit to the simulated $ m_{\ell\ell\gamma\gamma} $ distributions for a signal with $ m_{a}= $ 30 GeV in the electron (left) and muon (right) channels. |
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Figure 3-a:
Fit to the simulated $ m_{\ell\ell\gamma\gamma} $ distributions for a signal with $ m_{a}= $ 30 GeV in the electron (left) and muon (right) channels. |
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Figure 3-b:
Fit to the simulated $ m_{\ell\ell\gamma\gamma} $ distributions for a signal with $ m_{a}= $ 30 GeV in the electron (left) and muon (right) channels. |
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Figure 4:
Product of detector efficiency and analysis acceptance for signal samples with various $ m_{a} $. The denominator includes $ Z \rightarrow \mathrm{e}\mathrm{e}, \mu\mu, \tau\tau $ decay modes, and the numerator is the number of events after the full selection for $ Z \rightarrow \mathrm{e}\mathrm{e} $ (left) and $ \mu\mu $ (right) channel. The error bar shown here includes statistics and systematic uncertainty. The photon efficiency, lepton efficiency, and pile-up reweighting uncertainties are taken into account for the systematic uncertainty. |
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Figure 4-a:
Product of detector efficiency and analysis acceptance for signal samples with various $ m_{a} $. The denominator includes $ Z \rightarrow \mathrm{e}\mathrm{e}, \mu\mu, \tau\tau $ decay modes, and the numerator is the number of events after the full selection for $ Z \rightarrow \mathrm{e}\mathrm{e} $ (left) and $ \mu\mu $ (right) channel. The error bar shown here includes statistics and systematic uncertainty. The photon efficiency, lepton efficiency, and pile-up reweighting uncertainties are taken into account for the systematic uncertainty. |
png |
Figure 4-b:
Product of detector efficiency and analysis acceptance for signal samples with various $ m_{a} $. The denominator includes $ Z \rightarrow \mathrm{e}\mathrm{e}, \mu\mu, \tau\tau $ decay modes, and the numerator is the number of events after the full selection for $ Z \rightarrow \mathrm{e}\mathrm{e} $ (left) and $ \mu\mu $ (right) channel. The error bar shown here includes statistics and systematic uncertainty. The photon efficiency, lepton efficiency, and pile-up reweighting uncertainties are taken into account for the systematic uncertainty. |
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Figure 5:
Invariant mass $ m_{\ell\ell\gamma\gamma} $ distribution in data (black points). The background model fit is shown for $ m_{a} $ = 1 GeV (left) and 30 GeV (right), where the solid red line shows the background contribution. The lower panel shows the residuals after subtraction of this background component. The one (green) and two (yellow) standard deviation bands show the uncertainties in the fitted background model. |
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Figure 5-a:
Invariant mass $ m_{\ell\ell\gamma\gamma} $ distribution in data (black points). The background model fit is shown for $ m_{a} $ = 1 GeV (left) and 30 GeV (right), where the solid red line shows the background contribution. The lower panel shows the residuals after subtraction of this background component. The one (green) and two (yellow) standard deviation bands show the uncertainties in the fitted background model. |
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Figure 5-b:
Invariant mass $ m_{\ell\ell\gamma\gamma} $ distribution in data (black points). The background model fit is shown for $ m_{a} $ = 1 GeV (left) and 30 GeV (right), where the solid red line shows the background contribution. The lower panel shows the residuals after subtraction of this background component. The one (green) and two (yellow) standard deviation bands show the uncertainties in the fitted background model. |
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Figure 6:
Expected and observed 95 % CL limits on the product of the production cross section of the Higgs boson into di-photons and di-leptons via a Z boson and a pseudoscalar, $ \sigma (\mathrm{p}\mathrm{p} \to \mathrm{H})\times \mathcal{B}(\mathrm{H} \to \mathrm{Z} \mathrm{a} \to \ell\ell\gamma\gamma) $. The green (yellow) band represents the 68% (95%) CL expected limit intervals. |
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Figure 7:
Exclusion limits at 95% CL on $ C_{\mathrm{Z}\mathrm{H}}^\textrm{eff}/\Lambda $, assuming the ALP decays exclusively to a photon pair. The dashed black curve is the expected upper limit, with the one- and two-standard-deviation bands are shown in green and yellow, respectively. The solid black curve is the observed upper limit. |
| Tables | |
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Table 1:
Minimum BDT output values used to define the analysis categories, with the associated signal efficiencies and background yields. |
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Table 2:
Sources of systematic uncertainties and their magnitudes for each data taking period. |
| Summary |
| A search for Higgs boson decays to a Z boson and a pseudoscalar, which subsequently decay into a lepton pair and a photon pair, respectively, is presented. The analysis is based on proton-proton collision data collected at $ \sqrt{s} = $ 13 TeV by the CMS experiment in 2016, 2017, and 2018, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The analysis probes pseudoscalar masses in the range 1--30 GeV. This is the first search for Higgs boson decays in the final state of two leptons and two photons. No significant deviation from the background-only hypothesis is observed. Upper limits are set at 95% confidence level on the product of the production cross section of the Higgs boson and its branching fraction into a dilepton and a diphoton pair via a Z boson and a pseudoscalar, $ \sigma (\mathrm{p}\mathrm{p}\rightarrow \mathrm{H})\times \mathcal{B}(\mathrm{H}\to\mathrm{Z} a \to \ell\ell\gamma\gamma) $. The observed (expected) limit ranges from 17.8 (17.9) fb for $ m_{a} = $ 1 GeV to 4.7 (6.9) fb for $ m_{a} = $ 30 GeV. Constraints are also set on the axion-like-particle model parameter $ C_{ZH}^{eff}/\Lambda $, which describes the coupling between the Higgs boson, Z boson, and ALP. |
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