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CMS-PAS-HIG-21-014
Search for nonresonant Higgs boson pair production in the WW$ \gamma\gamma $ channel in pp collisions at $ \sqrt{s}= $ 13 TeV
Abstract: A search for nonresonant production of Higgs boson pairs in final states with two W bosons and two photons is presented. The search uses data from proton-proton collisions at a center-of-mass energy of $ \sqrt{s}= $ 13 TeV, recorded with the CMS detector at the LHC between 2016 and 2018, which correspond to an integrated luminosity of 138 fb$^{-1}$. This is the first search performed in this final state by the CMS collaboration. The observed (expected) 95% confidence level (CL) upper limit on Higgs boson pair production cross-section is evaluated to be 3.0 (1.6) pb, corresponding to about 97 (53) times the standard model prediction. Scans of modified SM and purely beyond SM (BSM) coupling parameters in an effective field theory framework result in an observed (expected) constraint on the Higgs boson self-coupling strength of -25.8 (-14.4) to 24.1 (18.3) times its SM value, and a constraint on the magnitude of a direct coupling of two top quarks to two Higgs bosons of -2.4 (-1.7) to 2.9 (2.2) at a 95% CL. Additionally, observed (expected) 95% CL upper limits are placed on twenty effective field theory BSM benchmark scenarios ranging from 1.7 to 6.2 (1.0 to 3.9) pb.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Feynman diagrams for leading-order Higgs boson pair production via ggF production.

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Figure 1-a:
Feynman diagrams for leading-order Higgs boson pair production via ggF production.

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Figure 1-b:
Feynman diagrams for leading-order Higgs boson pair production via ggF production.

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Figure 1-c:
Feynman diagrams for leading-order Higgs boson pair production via ggF production.

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Figure 1-d:
Feynman diagrams for leading-order Higgs boson pair production via ggF production.

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Figure 1-e:
Feynman diagrams for leading-order Higgs boson pair production via ggF production.

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Figure 2:
Data/MC comparison of the FH WW$ \gamma\gamma $ identifier DNN score in diphoton mass region 100 $ < m_{\gamma\gamma} < $ 180 GeV. Simulated background events are only used for the classifier training and not for the final signal extraction. MC statistical uncertainty is shown as grey shaded band, and data statistical uncertainty is shown as bar on the ratio points.

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Figure 3:
Data/MC comparison of the SL DNN score in diphoton mass region 100 $ < m_{\gamma\gamma} < $ 180 GeV. Simulated background events are only used for the classifier training and not for the final signal extraction. MC statistical uncertainty is shown as grey shaded band, and data statistical uncertainty is shown as bar on the ratio points.

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Figure 4:
Data/MC comparison of dilepton invariant mass $ m_{ll} $ in the FL channel after preselection. The main non-resonant background is the Drell-Yan process, and the main resonant background is the VH(H$ \rightarrow\gamma\gamma $) process, both concentrated in the region between 80 GeV and 100 GeV. Simulated backgrounds are only used in event selection optimization and not for the final signal extraction. MC statistical uncertainty is shown as grey shaded band, and data statistical uncertainty is shown as bar on the ratio points.

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Figure 5:
SL signal model, defined as a fit of a sum of up to five Gaussians in a binned $ m_{\gamma\gamma} $ distribution, in the most sensitive DNN category.

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Figure 6:
FH signal model, defined as a fit of a sum of up to five Gaussians in a binned $ m_{\gamma\gamma} $ distribution, in the second most sensitive DNN category.

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Figure 7:
FL signal model, defined as a fit of a sum of up to five Gaussians in a binned $ m_{\gamma\gamma} $ distribution.

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Figure 8:
The observed diphoton mass distribution including the signal plus background fit (red), the Single-Higgs + continuum background fit (blue) and the continuum background (black dashed line), with bands covering the $ \pm $1$\sigma $ and $ \pm $2$\sigma $ uncertainties in the fitted background. All analysis categories are combined and weighted by S$ / $(S$ + $B).

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Figure 9:
Run 2 95% CL limits on HH gluon fusion production with respect to $ \sigma_{SM}^{NLO} $ = 31.05 fb

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Figure 10:
95% CL upper limit scan of $ \kappa_{\lambda} $ hypotheses from -30 to 30, shown for each WW$ \gamma\gamma $ channel, and for the combined result.

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Figure 10-a:
95% CL upper limit scan of $ \kappa_{\lambda} $ hypotheses from -30 to 30, shown for each WW$ \gamma\gamma $ channel, and for the combined result.

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Figure 10-b:
95% CL upper limit scan of $ \kappa_{\lambda} $ hypotheses from -30 to 30, shown for each WW$ \gamma\gamma $ channel, and for the combined result.

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Figure 11:
95% CL upper limit scan of $ c_{2} $ hypotheses from -3 to 3, shown for each WW$ \gamma\gamma $ channel, and for the combined result.

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Figure 11-a:
95% CL upper limit scan of $ c_{2} $ hypotheses from -3 to 3, shown for each WW$ \gamma\gamma $ channel, and for the combined result.

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Figure 11-b:
95% CL upper limit scan of $ c_{2} $ hypotheses from -3 to 3, shown for each WW$ \gamma\gamma $ channel, and for the combined result.

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Figure 12:
Run 2 95% CL limits on HH gluon fusion production for different nonresonant benchmark models defined in Table 5.
Tables

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Table 1:
Parameter values of the 20 EFT benchmarks and the Standard Model.

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Table 2:
2017 simulated signal and background event yields (process efficiencies) before and after FH preselections.

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Table 3:
2017 simulated signal and background event yields (process efficiencies) before and after SL preselections.

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Table 4:
2017 simulated signal and background event yields (process efficiencies) before and after FL preselections.

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Table 5:
Upper limits on $ \frac{\sigma(HH)}{\sigma_{SM}(HH)} $, assuming an NLO cross-section prediction of $ \sigma_{SM}(HH) $ = 31.05 fb.
Summary
In this note, the first search for Higgs pair production in the WW$ \gamma\gamma $ final state performed by the CMS collaboration has been presented. The analysis makes use of data collected with the CMS detector between 2016 and 2018 corresponding to an integrated luminosity of 138 fb$^{-1}$, from proton-proton collisions at a center-of-mass energy of 13 TeV. Combining all final state categories, which makes use of all three WW decay modes, results in an observed (expected) 95% CL upper limit on the di-Higgs production cross-section of 3.0 (1.6) pb, corresponding to about 97 (53) times the standard model prediction. Scans of modified SM and purely BSM coupling parameters in an EFT framework result in an observed (expected) constraint on the Higgs self-coupling of -25.8 (-14.4) to 24.1 (18.3) times its standard model value, and a constraint on the magnitude of the direct coupling of two top quarks to two Higgs bosons of -2.4 (-1.7) to 2.9 (2.2) at a 95% CL. Additionally, observed (expected) 95% CL upper limits are placed on twenty EFT benchmark scenarios ranging from 1.7 - 6.2 (1.0 - 3.9) pb.
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Compact Muon Solenoid
LHC, CERN