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| CMS-PAS-B2G-21-001 | ||
| Search for Higgs boson pair production via vector boson fusion with highly Lorentz-boosted Higgs bosons in the four b quark final state at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| July 2021 | ||
| Abstract: Nonresonant Higgs boson pair production via vector boson fusion is searched for in the final state where each Higgs boson decays to a b quark-antiquark pair, and both Higgs bosons are highly Lorentz boosted so that they can be reconstructed as two large-radius jets. The data collected by the CMS experiment in 2016-2018 from proton-proton collisions at a centre-of-mass energy of 13 TeV is used, corresponding to an integrated luminosity of 138 fb$^{-1}$. A novel multivariate classifier based on graph neural networks, ParticleNet, is applied to identify the jets that contain the Higgs boson decay products. No excess is observed compared to the background-only expectation, and upper limits are set on the product of the nonresonant Higgs boson pair production cross section via vector boson fusion and the branching fraction into $\textrm{b}\bar{\textrm{b}}\textrm{b}\bar{\textrm{b}}$. The strength of the coupling between a pair of Higgs bosons and a pair of vector bosons relative to the standard model coupling is constrained within the range 0.6 $ < \kappa_{\textrm{2V}} < $ 1.4 at 95% confidence level when all other Higgs boson couplings are assumed equal to their standard model values. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Leading-order diagrams for nonresonant HH production via vector boson fusion. |
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Figure 1-a:
Leading-order diagrams for nonresonant HH production via vector boson fusion. |
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Figure 1-b:
Leading-order diagrams for nonresonant HH production via vector boson fusion. |
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Figure 1-c:
Leading-order diagrams for nonresonant HH production via vector boson fusion. |
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Figure 2:
The distributions of the invariant mass of the HH system after a background-only fit to the data, for the high-purity (upper), medium-purity (middle), and low-purity (lower) categories. |
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Figure 2-a:
The distributions of the invariant mass of the HH system after a background-only fit to the data, for the high-purity (upper), medium-purity (middle), and low-purity (lower) categories. |
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Figure 2-b:
The distributions of the invariant mass of the HH system after a background-only fit to the data, for the high-purity (upper), medium-purity (middle), and low-purity (lower) categories. |
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Figure 2-c:
The distributions of the invariant mass of the HH system after a background-only fit to the data, for the high-purity (upper), medium-purity (middle), and low-purity (lower) categories. |
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Figure 3:
Observed (solid line) and expected (dashed line) 95% CL exclusion limit on the product of the VBF HH production cross section and the branching fraction into ${\mathrm{b} \mathrm{\bar{b}} \mathrm{b} \mathrm{\bar{b}}}$, as a function of the ${\kappa _{\textrm {2V}}}$ coupling, with other couplings fixed to the SM values. The crossings of observed limit and the theoretical cross section (red line) indicate the ranges of the coupling values excluded at 95% CL. |
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Figure 4:
Observed (solid line) and expected (dashed line) 95% CL exclusion limit on the product of the VBF HH production cross section and the branching fraction into ${\mathrm{b} \mathrm{\bar{b}} \mathrm{b} \mathrm{\bar{b}}}$, as a function of the ${\kappa _{\textrm {V}}}$ coupling, with other couplings fixed to the SM values. The crossings of observed limit and the theoretical cross section (red line) indicate the ranges of the coupling values excluded at 95% CL. |
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Figure 5:
Observed (solid line) and expected (dashed line) 95% CL exclusion limit on the product of the VBF HH production cross section and the branching fraction into ${\mathrm{b} \mathrm{\bar{b}} \mathrm{b} \mathrm{\bar{b}}}$, as a function of the ${\kappa _{\textrm {2V}}}$ coupling, with the ${\kappa _{\textrm {V}}}$ coupling fixed to a values of 0.8 (upper) and 1.2 (lower), while other couplings are fixed to the SM values. The crossings of observed limit and the theoretical cross section (red line) indicate the ranges of the coupling values excluded at 95% CL. |
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Figure 5-a:
Observed (solid line) and expected (dashed line) 95% CL exclusion limit on the product of the VBF HH production cross section and the branching fraction into ${\mathrm{b} \mathrm{\bar{b}} \mathrm{b} \mathrm{\bar{b}}}$, as a function of the ${\kappa _{\textrm {2V}}}$ coupling, with the ${\kappa _{\textrm {V}}}$ coupling fixed to a values of 0.8 (upper) and 1.2 (lower), while other couplings are fixed to the SM values. The crossings of observed limit and the theoretical cross section (red line) indicate the ranges of the coupling values excluded at 95% CL. |
png pdf |
Figure 5-b:
Observed (solid line) and expected (dashed line) 95% CL exclusion limit on the product of the VBF HH production cross section and the branching fraction into ${\mathrm{b} \mathrm{\bar{b}} \mathrm{b} \mathrm{\bar{b}}}$, as a function of the ${\kappa _{\textrm {2V}}}$ coupling, with the ${\kappa _{\textrm {V}}}$ coupling fixed to a values of 0.8 (upper) and 1.2 (lower), while other couplings are fixed to the SM values. The crossings of observed limit and the theoretical cross section (red line) indicate the ranges of the coupling values excluded at 95% CL. |
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Figure 6:
Observed (solid lines) and expected (dashed lines) 95% CL exclusion limits as a function of the ${\kappa _{\textrm {2V}}}$ and ${\kappa _{\textrm {V}}}$ couplings, obtained with the CL$_{\text {s}}$ method, assuming all the other couplings to be fixed to the SM values. The hatched regions are excluded by the observed limits. The dotted curves indicate theoretical VBF HH production cross section predictions as a function of the two couplings. The SM prediction is shown as a red marker. |
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Figure 7:
Observed values of likelihood as a function of the ${\kappa _{\textrm {2V}}}$ and ${\kappa _{\textrm {V}}}$ couplings, assuming all the other couplings to be fixed to the SM values. The dashed and dotted contours indicate the regions allowed at the 68 and 95% CL, respectively. The SM prediction is shown as a red marker. |
| Tables | |
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Table 1:
Summary of selections that define the search region. |
| Summary |
| Nonresonant Higgs boson pair production via vector boson fusion is searched for in the final state where each Higgs boson decays to a b quark-antiquark pair, using data from proton-proton collisions at a centre-of-mass energy of 13 TeV, collected by the CMS experiment in 2016-2018 and corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis focuses on the phase space region where both Higgs bosons are highly Lorentz-boosted, so that the two Higgs boson decays can be reconstructed as two large-radius jets. The two large-radius jets with the highest transverse momentum are considered as the Higgs boson candidates. The analysis is the first one to target such boosted topology in search for nonresonant VBF {cmsSymbolFace{H}}hbbbb process, and the first one to apply a novel multivariate classifier based on graph convolutional neural networks, ParticleNet, to identify the jets that correspond to ${\textrm{H} \rightarrow \mathrm{ b\bar{b} }} $ decays. The data are found to agree with the background-only hypothesis, and upper limits on the production cross section are presented as a function of the coupling between a pair of Higgs bosons and a pair of vector bosons, ${\kappa_{\textrm{2V}}} $, and the coupling between one Higgs boson and a pair of vector bosons, ${\kappa_{\textrm{V}}} $, normalized to the coupling values predicted in the standard model. The observed (expected) limits constrain ${\kappa_{\textrm{2V}}} $ within the range 0.6 $ < {\kappa_{\textrm{2V}}} < $ 1.4 (0.6 $ < {\kappa_{\textrm{2V}}} < $ 1.4) and ${\kappa_{\textrm{V}}} $ within $-$1.2 $ < {\kappa_{\textrm{V}}} < $ $-$0.8 or 0.8 $ < {\kappa_{\textrm{V}}} < $ 1.2 ($-$1.2 $ < {\kappa_{\textrm{V}}} < $ $-$0.8 or 0.8 $ < {\kappa_{\textrm{V}}} < $ 1.2) at 95% confidence level, when all other Higgs boson couplings are assumed equal to their standard model values. The signal hypothesis with ${\kappa_{\textrm{2V}}} =$ 0 and other couplings equal to 1 is excluded at a CL higher than 99.99%. When both ${\kappa_{\textrm{2V}}} $ and ${\kappa_{\textrm{V}}} $ are varied simultaneously, the observed limits exclude the hypothesis ${\kappa_{\textrm{2V}}} =$ 0 at a CL of 95% or higher for all ${\kappa_{\textrm{V}}} $ coupling values above 0.5, with other couplings assumed equal to their standard model values. |
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