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| CMS-PAS-HIG-21-003 | ||
| Search for exotic decay of the Higgs boson into two light pseudoscalars with four photons in the final state at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| July 2021 | ||
| Abstract: A search for exotic decays of the Higgs boson to a pair of light pseudoscalars, each of which subsequently decay to a pair of photons, is presented. The search uses data from proton-proton collisions at $\sqrt{s} = $ 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 132 fb$^{-1}$. The analysis considers inclusive production mode of the Higgs boson, and probes pseudoscalars ($a$) that range in mass from 15 $ < m_{a} < $ 60 GeV, and leads to four well isolated photons in the final state. No significant deviation from the background-only hypothesis is observed, and upper limits are set on the product of the Higgs boson production cross section and branching fraction into four photons. The observed (expected) limits range from 0.80 (1.00) fb for $m_{a} = $ 15 GeV to 0.33 (0.30) fb for $m_{a} = $ 60 GeV at the 95% confidence level. | ||
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These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Feynman diagram for BSM decay of the Higgs boson into a pair of light pseudoscalars, which further decay to photons. |
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Figure 2:
Distributions of the four most highly ranked discriminating variables: difference between invariant mass of the pseudoscalar and the m(a)$_{hyp}$ parameter divided by the invariant mass of the four-photon system (top left), difference between invariant mass of the pseudoscalars (top right), photon ID of the 3rd photon (bottom left), and photon ID of the 4th photon (bottom right). Events shown are selected after fulfilling the selection criteria described in Section 4, and from the ${m_{\gamma \gamma \gamma \gamma}}$ sidebands, satisfying either 110 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 115 GeV or 135 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 180 GeV. The output of the BDT for the signal simulated at various pseudoscalar mass hypotheses are also shown. The disagreement between event mixing data set and data only results in a sub-optimal performance of the classifier and does not induce any biases in the analysis. |
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Figure 2-a:
Distributions of the four most highly ranked discriminating variables: difference between invariant mass of the pseudoscalar and the m(a)$_{hyp}$ parameter divided by the invariant mass of the four-photon system (top left), difference between invariant mass of the pseudoscalars (top right), photon ID of the 3rd photon (bottom left), and photon ID of the 4th photon (bottom right). Events shown are selected after fulfilling the selection criteria described in Section 4, and from the ${m_{\gamma \gamma \gamma \gamma}}$ sidebands, satisfying either 110 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 115 GeV or 135 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 180 GeV. The output of the BDT for the signal simulated at various pseudoscalar mass hypotheses are also shown. The disagreement between event mixing data set and data only results in a sub-optimal performance of the classifier and does not induce any biases in the analysis. |
png pdf |
Figure 2-b:
Distributions of the four most highly ranked discriminating variables: difference between invariant mass of the pseudoscalar and the m(a)$_{hyp}$ parameter divided by the invariant mass of the four-photon system (top left), difference between invariant mass of the pseudoscalars (top right), photon ID of the 3rd photon (bottom left), and photon ID of the 4th photon (bottom right). Events shown are selected after fulfilling the selection criteria described in Section 4, and from the ${m_{\gamma \gamma \gamma \gamma}}$ sidebands, satisfying either 110 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 115 GeV or 135 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 180 GeV. The output of the BDT for the signal simulated at various pseudoscalar mass hypotheses are also shown. The disagreement between event mixing data set and data only results in a sub-optimal performance of the classifier and does not induce any biases in the analysis. |
png pdf |
Figure 2-c:
Distributions of the four most highly ranked discriminating variables: difference between invariant mass of the pseudoscalar and the m(a)$_{hyp}$ parameter divided by the invariant mass of the four-photon system (top left), difference between invariant mass of the pseudoscalars (top right), photon ID of the 3rd photon (bottom left), and photon ID of the 4th photon (bottom right). Events shown are selected after fulfilling the selection criteria described in Section 4, and from the ${m_{\gamma \gamma \gamma \gamma}}$ sidebands, satisfying either 110 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 115 GeV or 135 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 180 GeV. The output of the BDT for the signal simulated at various pseudoscalar mass hypotheses are also shown. The disagreement between event mixing data set and data only results in a sub-optimal performance of the classifier and does not induce any biases in the analysis. |
png pdf |
Figure 2-d:
Distributions of the four most highly ranked discriminating variables: difference between invariant mass of the pseudoscalar and the m(a)$_{hyp}$ parameter divided by the invariant mass of the four-photon system (top left), difference between invariant mass of the pseudoscalars (top right), photon ID of the 3rd photon (bottom left), and photon ID of the 4th photon (bottom right). Events shown are selected after fulfilling the selection criteria described in Section 4, and from the ${m_{\gamma \gamma \gamma \gamma}}$ sidebands, satisfying either 110 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 115 GeV or 135 $ < {m_{\gamma \gamma \gamma \gamma}} < $ 180 GeV. The output of the BDT for the signal simulated at various pseudoscalar mass hypotheses are also shown. The disagreement between event mixing data set and data only results in a sub-optimal performance of the classifier and does not induce any biases in the analysis. |
png pdf |
Figure 3:
Distribution of the BDT output for ${m_{a}} = $ 15 GeV (left) and 50 GeV (right) in data and simulated events. Events shown are selected after fulfilling the selection criteria described in Section 4, and from the ${m_{\gamma \gamma \gamma \gamma}} $ sidebands, satisfying either 110 $ < m_{\gamma \gamma \gamma \gamma} < $ 115 GeV or 135 $ < m_{\gamma \gamma \gamma \gamma} < $ 180 GeV. |
png pdf |
Figure 3-a:
Distribution of the BDT output for ${m_{a}} = $ 15 GeV (left) and 50 GeV (right) in data and simulated events. Events shown are selected after fulfilling the selection criteria described in Section 4, and from the ${m_{\gamma \gamma \gamma \gamma}} $ sidebands, satisfying either 110 $ < m_{\gamma \gamma \gamma \gamma} < $ 115 GeV or 135 $ < m_{\gamma \gamma \gamma \gamma} < $ 180 GeV. |
png pdf |
Figure 3-b:
Distribution of the BDT output for ${m_{a}} = $ 15 GeV (left) and 50 GeV (right) in data and simulated events. Events shown are selected after fulfilling the selection criteria described in Section 4, and from the ${m_{\gamma \gamma \gamma \gamma}} $ sidebands, satisfying either 110 $ < m_{\gamma \gamma \gamma \gamma} < $ 115 GeV or 135 $ < m_{\gamma \gamma \gamma \gamma} < $ 180 GeV. |
png pdf |
Figure 4:
Parametrized signal shape for m(a) = 15 GeV is shown for 2016 (top left), 2017 (top right), and 2018 (bottom). Separate signal models are built for each of the three data taking years, which are then scaled by the appropriate luminosity and summed in order to construct the final signal model. The open squares represent simulated events and the blue lines are the corresponding models. Also shown are the $\sigma _{\text {eff}}$ value (half the width of the narrowest interval containing 68.3% of the invariant mass distribution) with the corresponding interval as a gray band, and the full width at half the maximum (FWHM) with the corresponding interval as a double arrow. |
png pdf |
Figure 4-a:
Parametrized signal shape for m(a) = 15 GeV is shown for 2016 (top left), 2017 (top right), and 2018 (bottom). Separate signal models are built for each of the three data taking years, which are then scaled by the appropriate luminosity and summed in order to construct the final signal model. The open squares represent simulated events and the blue lines are the corresponding models. Also shown are the $\sigma _{\text {eff}}$ value (half the width of the narrowest interval containing 68.3% of the invariant mass distribution) with the corresponding interval as a gray band, and the full width at half the maximum (FWHM) with the corresponding interval as a double arrow. |
png pdf |
Figure 4-b:
Parametrized signal shape for m(a) = 15 GeV is shown for 2016 (top left), 2017 (top right), and 2018 (bottom). Separate signal models are built for each of the three data taking years, which are then scaled by the appropriate luminosity and summed in order to construct the final signal model. The open squares represent simulated events and the blue lines are the corresponding models. Also shown are the $\sigma _{\text {eff}}$ value (half the width of the narrowest interval containing 68.3% of the invariant mass distribution) with the corresponding interval as a gray band, and the full width at half the maximum (FWHM) with the corresponding interval as a double arrow. |
png pdf |
Figure 4-c:
Parametrized signal shape for m(a) = 15 GeV is shown for 2016 (top left), 2017 (top right), and 2018 (bottom). Separate signal models are built for each of the three data taking years, which are then scaled by the appropriate luminosity and summed in order to construct the final signal model. The open squares represent simulated events and the blue lines are the corresponding models. Also shown are the $\sigma _{\text {eff}}$ value (half the width of the narrowest interval containing 68.3% of the invariant mass distribution) with the corresponding interval as a gray band, and the full width at half the maximum (FWHM) with the corresponding interval as a double arrow. |
png pdf |
Figure 5:
Parametrized signal shape for m(a) = 50 GeV is shown for 2016 (top left), 2017 (top right), and 2018 (bottom). Separate signal models are built for each of the three data taking years, which are then scaled by the appropriate luminosity and summed in order to construct the final signal model. The open squares represent simulated events and the blue lines are the corresponding models. Also shown are the $\sigma _{\text {eff}}$ value (half the width of the narrowest interval containing 68.3% of the invariant mass distribution) with the corresponding interval as a gray band, and the full width at half the maximum (FWHM) with the corresponding interval as a double arrow. |
png pdf |
Figure 5-a:
Parametrized signal shape for m(a) = 50 GeV is shown for 2016 (top left), 2017 (top right), and 2018 (bottom). Separate signal models are built for each of the three data taking years, which are then scaled by the appropriate luminosity and summed in order to construct the final signal model. The open squares represent simulated events and the blue lines are the corresponding models. Also shown are the $\sigma _{\text {eff}}$ value (half the width of the narrowest interval containing 68.3% of the invariant mass distribution) with the corresponding interval as a gray band, and the full width at half the maximum (FWHM) with the corresponding interval as a double arrow. |
png pdf |
Figure 5-b:
Parametrized signal shape for m(a) = 50 GeV is shown for 2016 (top left), 2017 (top right), and 2018 (bottom). Separate signal models are built for each of the three data taking years, which are then scaled by the appropriate luminosity and summed in order to construct the final signal model. The open squares represent simulated events and the blue lines are the corresponding models. Also shown are the $\sigma _{\text {eff}}$ value (half the width of the narrowest interval containing 68.3% of the invariant mass distribution) with the corresponding interval as a gray band, and the full width at half the maximum (FWHM) with the corresponding interval as a double arrow. |
png pdf |
Figure 5-c:
Parametrized signal shape for m(a) = 50 GeV is shown for 2016 (top left), 2017 (top right), and 2018 (bottom). Separate signal models are built for each of the three data taking years, which are then scaled by the appropriate luminosity and summed in order to construct the final signal model. The open squares represent simulated events and the blue lines are the corresponding models. Also shown are the $\sigma _{\text {eff}}$ value (half the width of the narrowest interval containing 68.3% of the invariant mass distribution) with the corresponding interval as a gray band, and the full width at half the maximum (FWHM) with the corresponding interval as a double arrow. |
png pdf |
Figure 6:
Invariant mass distribution, ${m_{\gamma \gamma \gamma \gamma}}$, for data (black points) and signal-plus-background model fit is shown for ${m_{a}} = $ 15 GeV (left) and $ {m_{a}} = $ 50 GeV (right). The solid red line shows the total signal-plus-background contribution, whereas the dashed red line shows the background component only. The lower panel shows the residuals after subtraction of this background component. The one (green) and two (yellow) standard deviation bands include the uncertainties in the background component of the fit. The lower panel in each plot shows the residual signal yield after the background subtraction. |
png pdf |
Figure 6-a:
Invariant mass distribution, ${m_{\gamma \gamma \gamma \gamma}}$, for data (black points) and signal-plus-background model fit is shown for ${m_{a}} = $ 15 GeV (left) and $ {m_{a}} = $ 50 GeV (right). The solid red line shows the total signal-plus-background contribution, whereas the dashed red line shows the background component only. The lower panel shows the residuals after subtraction of this background component. The one (green) and two (yellow) standard deviation bands include the uncertainties in the background component of the fit. The lower panel in each plot shows the residual signal yield after the background subtraction. |
png pdf |
Figure 6-b:
Invariant mass distribution, ${m_{\gamma \gamma \gamma \gamma}}$, for data (black points) and signal-plus-background model fit is shown for ${m_{a}} = $ 15 GeV (left) and $ {m_{a}} = $ 50 GeV (right). The solid red line shows the total signal-plus-background contribution, whereas the dashed red line shows the background component only. The lower panel shows the residuals after subtraction of this background component. The one (green) and two (yellow) standard deviation bands include the uncertainties in the background component of the fit. The lower panel in each plot shows the residual signal yield after the background subtraction. |
png pdf |
Figure 7:
Expected and observed 95% CL limits on the product of the production cross section of the Higgs boson and the branching fraction into four photons via a pair of pseuodscalars, ${\sigma _{\mathrm{H}}} \times {\mathcal {B}({\mathrm{H} \rightarrow aa \rightarrow \gamma \gamma \gamma \gamma})}$, is shown as a function of ${m_{a}}$. The green (yellow) bands represent the 68% (95%) expected limit intervals. |
| Tables | |
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Table 1:
Summary of the minimum BDT output value and efficiency with respect to a selection on BDT output for each nominal signal hypothesis. |
| Summary |
| A search for a pair of light pseudoscalars that subsequently decay into photons produced from decays of the 125 GeV Higgs boson is presented. The analysis is based on the proton-proton collision data collected at $\sqrt{s} = $ 13 TeV by the CMS experiment at the LHC in 2016, 2017, and 2018, which corresponds to a total integrated luminosity of 131.2 fb$^{-1}$. The analysis probes pseudoscalars ranging in mass from 15 to 60 GeV. In absence of any significant deviation from the background-only hypothesis, upper limits are set at 95% CL on the product of the production cross section of the Higgs boson and the branching fraction into four photons via a pair of pseuodscalars, $\sigma_{\mathrm{H}} \times$ BR. The observed (expected) limit ranges from 0.80 (1.00) fb for $m_a =$ 15 GeV to 0.33 (0.30) fb for $m_a =$ 60 GeV. |
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