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| CMS-HIG-21-002 ; CERN-EP-2022-113 | ||
| Search for Higgs boson pairs decaying to WWWW, WW$\tau\tau$, and $\tau\tau\tau\tau$ in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 21 June 2022 | ||
| JHEP 07 (2023) 095 | ||
| Abstract: The results of a search for Higgs boson pair (HH) production in the WWWW, WW$\tau\tau$, and $\tau\tau\tau\tau$ decay modes are presented. The search uses 138 fb$^{-1}$ of proton-proton collision data recorded by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV from 2016 to 2018. Analyzed events contain two, three, or four reconstructed leptons, including electrons, muons, and hadronically decaying tau leptons. No evidence for a signal is found in the data. Upper limits are set on the cross section for nonresonant HH production, as well as resonant production in which a new heavy particle decays to a pair of Higgs bosons. For nonresonant production, the observed (expected) upper limit on the cross section at 95% confidence level (CL) is 21.3 (19.4) times the standard model (SM) prediction. The observed (expected) ratio of the trilinear Higgs boson self-coupling to its value in the SM is constrained to be within the interval $-$6.9 to 11.1 ($-$6.9 to 11.7) at 95% CL, and limits are set on a variety of new-physics models using an effective field theory approach. The observed (expected) limits on the cross section for resonant HH production amount to 0.18-0.90 (0.08-1.06) pb at 95% CL for new heavy-particle masses in the range 250-1000 GeV. | ||
| Links: e-print arXiv:2206.10268 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; Physics Briefing ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Leading order Feynman diagrams for SM nonresonant HH production via gluon fusion, including the "triangle'' diagram (left) and the "box'' diagram (right). |
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Figure 1-a:
Leading order Feynman diagrams for SM nonresonant HH production via gluon fusion, including the "triangle'' diagram (left) and the "box'' diagram (right). |
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Figure 1-b:
Leading order Feynman diagrams for SM nonresonant HH production via gluon fusion, including the "triangle'' diagram (left) and the "box'' diagram (right). |
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Figure 2:
Leading order Feynman diagrams for nonresonant HH production via gluon fusion in an EFT approach, where loop-mediated contact interactions between (left) two gluons and one H boson, (middle) two gluons and two H bosons, and (right) two top quarks and two H bosons are parametrized by three effective couplings: ${\text {c}_{{\mathrm{g}}}}$, ${\text {c}_{2 {\mathrm{g}}}}$, and ${\text {c}_{2}}$. |
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Figure 2-a:
Leading order Feynman diagrams for nonresonant HH production via gluon fusion in an EFT approach, where loop-mediated contact interactions between (left) two gluons and one H boson, (middle) two gluons and two H bosons, and (right) two top quarks and two H bosons are parametrized by three effective couplings: ${\text {c}_{{\mathrm{g}}}}$, ${\text {c}_{2 {\mathrm{g}}}}$, and ${\text {c}_{2}}$. |
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Figure 2-b:
Leading order Feynman diagrams for nonresonant HH production via gluon fusion in an EFT approach, where loop-mediated contact interactions between (left) two gluons and one H boson, (middle) two gluons and two H bosons, and (right) two top quarks and two H bosons are parametrized by three effective couplings: ${\text {c}_{{\mathrm{g}}}}$, ${\text {c}_{2 {\mathrm{g}}}}$, and ${\text {c}_{2}}$. |
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Figure 2-c:
Leading order Feynman diagrams for nonresonant HH production via gluon fusion in an EFT approach, where loop-mediated contact interactions between (left) two gluons and one H boson, (middle) two gluons and two H bosons, and (right) two top quarks and two H bosons are parametrized by three effective couplings: ${\text {c}_{{\mathrm{g}}}}$, ${\text {c}_{2 {\mathrm{g}}}}$, and ${\text {c}_{2}}$. |
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Figure 3:
Leading order Feynman diagram for resonant HH production. |
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Figure 4:
Distributions in a few observables used as inputs to the BDT classifiers in the 2$\ell$ss and 3$\ell$ categories: the scalar ${p_{\mathrm {T}}}$ sum, denoted as ${H_{\mathrm {T}}}$, of the two reconstructed ${\ell}$ and all small-radius jets in the 2$\ell$ss category (upper left); the angular separation $\Delta R$ between the two ${\ell}$ in the 2$\ell$ss category (upper right); the angular separation between $ {\ell} _{3}$ and the nearest small-radius jet in the 3$\ell$ category (lower left); and ${{p_{\mathrm {T}}} ^\text {miss,LD}}$ in the 3$\ell$ category (lower right). The $ {\ell} _{3}$ in the 3$\ell$ category is defined as the ${\ell}$ that is not part of the opposite-sign ${\ell \ell}$ pair of lowest mass. The distributions expected for the different background processes are shown for the values of nuisance parameters obtained from the background-only ML fit, in which the HH signal is constrained to be zero. |
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Figure 4-a:
Distributions in a few observables used as inputs to the BDT classifiers in the 2$\ell$ss and 3$\ell$ categories: the scalar ${p_{\mathrm {T}}}$ sum, denoted as ${H_{\mathrm {T}}}$, of the two reconstructed ${\ell}$ and all small-radius jets in the 2$\ell$ss category (upper left); the angular separation $\Delta R$ between the two ${\ell}$ in the 2$\ell$ss category (upper right); the angular separation between $ {\ell} _{3}$ and the nearest small-radius jet in the 3$\ell$ category (lower left); and ${{p_{\mathrm {T}}} ^\text {miss,LD}}$ in the 3$\ell$ category (lower right). The $ {\ell} _{3}$ in the 3$\ell$ category is defined as the ${\ell}$ that is not part of the opposite-sign ${\ell \ell}$ pair of lowest mass. The distributions expected for the different background processes are shown for the values of nuisance parameters obtained from the background-only ML fit, in which the HH signal is constrained to be zero. |
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Figure 4-b:
Distributions in a few observables used as inputs to the BDT classifiers in the 2$\ell$ss and 3$\ell$ categories: the scalar ${p_{\mathrm {T}}}$ sum, denoted as ${H_{\mathrm {T}}}$, of the two reconstructed ${\ell}$ and all small-radius jets in the 2$\ell$ss category (upper left); the angular separation $\Delta R$ between the two ${\ell}$ in the 2$\ell$ss category (upper right); the angular separation between $ {\ell} _{3}$ and the nearest small-radius jet in the 3$\ell$ category (lower left); and ${{p_{\mathrm {T}}} ^\text {miss,LD}}$ in the 3$\ell$ category (lower right). The $ {\ell} _{3}$ in the 3$\ell$ category is defined as the ${\ell}$ that is not part of the opposite-sign ${\ell \ell}$ pair of lowest mass. The distributions expected for the different background processes are shown for the values of nuisance parameters obtained from the background-only ML fit, in which the HH signal is constrained to be zero. |
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Figure 4-c:
Distributions in a few observables used as inputs to the BDT classifiers in the 2$\ell$ss and 3$\ell$ categories: the scalar ${p_{\mathrm {T}}}$ sum, denoted as ${H_{\mathrm {T}}}$, of the two reconstructed ${\ell}$ and all small-radius jets in the 2$\ell$ss category (upper left); the angular separation $\Delta R$ between the two ${\ell}$ in the 2$\ell$ss category (upper right); the angular separation between $ {\ell} _{3}$ and the nearest small-radius jet in the 3$\ell$ category (lower left); and ${{p_{\mathrm {T}}} ^\text {miss,LD}}$ in the 3$\ell$ category (lower right). The $ {\ell} _{3}$ in the 3$\ell$ category is defined as the ${\ell}$ that is not part of the opposite-sign ${\ell \ell}$ pair of lowest mass. The distributions expected for the different background processes are shown for the values of nuisance parameters obtained from the background-only ML fit, in which the HH signal is constrained to be zero. |
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Figure 4-d:
Distributions in a few observables used as inputs to the BDT classifiers in the 2$\ell$ss and 3$\ell$ categories: the scalar ${p_{\mathrm {T}}}$ sum, denoted as ${H_{\mathrm {T}}}$, of the two reconstructed ${\ell}$ and all small-radius jets in the 2$\ell$ss category (upper left); the angular separation $\Delta R$ between the two ${\ell}$ in the 2$\ell$ss category (upper right); the angular separation between $ {\ell} _{3}$ and the nearest small-radius jet in the 3$\ell$ category (lower left); and ${{p_{\mathrm {T}}} ^\text {miss,LD}}$ in the 3$\ell$ category (lower right). The $ {\ell} _{3}$ in the 3$\ell$ category is defined as the ${\ell}$ that is not part of the opposite-sign ${\ell \ell}$ pair of lowest mass. The distributions expected for the different background processes are shown for the values of nuisance parameters obtained from the background-only ML fit, in which the HH signal is constrained to be zero. |
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Figure 5:
Distributions in ${m_{\mathrm {T}}}$ in the 3$\ell$WZ CR (left) and in $m_{4 {\ell}}$ in the 4$\ell$ZZ CR (right). The distributions expected for the WZ and ZZ as well as for other background processes are shown for the values of nuisance parameters obtained from the ML fit described in Section 9. |
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Figure 5-a:
Distributions in ${m_{\mathrm {T}}}$ in the 3$\ell$WZ CR (left) and in $m_{4 {\ell}}$ in the 4$\ell$ZZ CR (right). The distributions expected for the WZ and ZZ as well as for other background processes are shown for the values of nuisance parameters obtained from the ML fit described in Section 9. |
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Figure 5-b:
Distributions in ${m_{\mathrm {T}}}$ in the 3$\ell$WZ CR (left) and in $m_{4 {\ell}}$ in the 4$\ell$ZZ CR (right). The distributions expected for the WZ and ZZ as well as for other background processes are shown for the values of nuisance parameters obtained from the ML fit described in Section 9. |
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Figure 6:
Distributions in ${m_{\mathrm {T}}}$ in the 2$\ell$ss CR (left) and in the mass of the HH candidate in the 2${\ell}$+2${\tau _\mathrm {h}}$ CR (right). The distributions expected for the misidentified ${\ell} $/${\tau _\mathrm {h}}$ background as well as for other background processes are shown for the values of nuisance parameters obtained from the background-only ML fit, in which the HH signal is constrained to be zero. |
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Figure 6-a:
Distributions in ${m_{\mathrm {T}}}$ in the 2$\ell$ss CR (left) and in the mass of the HH candidate in the 2${\ell}$+2${\tau _\mathrm {h}}$ CR (right). The distributions expected for the misidentified ${\ell} $/${\tau _\mathrm {h}}$ background as well as for other background processes are shown for the values of nuisance parameters obtained from the background-only ML fit, in which the HH signal is constrained to be zero. |
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Figure 6-b:
Distributions in ${m_{\mathrm {T}}}$ in the 2$\ell$ss CR (left) and in the mass of the HH candidate in the 2${\ell}$+2${\tau _\mathrm {h}}$ CR (right). The distributions expected for the misidentified ${\ell} $/${\tau _\mathrm {h}}$ background as well as for other background processes are shown for the values of nuisance parameters obtained from the background-only ML fit, in which the HH signal is constrained to be zero. |
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Figure 7:
Distribution in the output of the BDT trained for nonresonant HH production and evaluated for the benchmark scenario JHEP04 BM7 for the 2$\ell$ss (upper left), 3$\ell$ (upper right), and 4$\ell$ (lower) categories. The SM HH signal is shown for a cross section amounting to 30 times the value predicted in the SM. The distributions expected for the background processes are shown for the values of nuisance parameters obtained from the ML fit of the signal+background hypothesis to the data. |
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Figure 7-a:
Distribution in the output of the BDT trained for nonresonant HH production and evaluated for the benchmark scenario JHEP04 BM7 for the 2$\ell$ss (upper left), 3$\ell$ (upper right), and 4$\ell$ (lower) categories. The SM HH signal is shown for a cross section amounting to 30 times the value predicted in the SM. The distributions expected for the background processes are shown for the values of nuisance parameters obtained from the ML fit of the signal+background hypothesis to the data. |
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Figure 7-b:
Distribution in the output of the BDT trained for nonresonant HH production and evaluated for the benchmark scenario JHEP04 BM7 for the 2$\ell$ss (upper left), 3$\ell$ (upper right), and 4$\ell$ (lower) categories. The SM HH signal is shown for a cross section amounting to 30 times the value predicted in the SM. The distributions expected for the background processes are shown for the values of nuisance parameters obtained from the ML fit of the signal+background hypothesis to the data. |
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Figure 7-c:
Distribution in the output of the BDT trained for nonresonant HH production and evaluated for the benchmark scenario JHEP04 BM7 for the 2$\ell$ss (upper left), 3$\ell$ (upper right), and 4$\ell$ (lower) categories. The SM HH signal is shown for a cross section amounting to 30 times the value predicted in the SM. The distributions expected for the background processes are shown for the values of nuisance parameters obtained from the ML fit of the signal+background hypothesis to the data. |
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Figure 8:
Distribution in the output of the BDT trained for nonresonant HH production and evaluated for the benchmark scenario JHEP04 BM7 for the 3${\ell}$+1${\tau _\mathrm {h}}$ (upper left), 2${\ell}$+2${\tau _\mathrm {h}}$ (upper right), 1${\ell}$+3${\tau _\mathrm {h}}$ (lower left), and 4${\tau _\mathrm {h}}$ (lower right) categories. The SM HH signal is shown for a cross section amounting to 30 times the value predicted in the SM. The distributions expected for the background processes are shown for the values of nuisance parameters obtained from the ML fit of the signal+background hypothesis to the data. |
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Figure 8-a:
Distribution in the output of the BDT trained for nonresonant HH production and evaluated for the benchmark scenario JHEP04 BM7 for the 3${\ell}$+1${\tau _\mathrm {h}}$ (upper left), 2${\ell}$+2${\tau _\mathrm {h}}$ (upper right), 1${\ell}$+3${\tau _\mathrm {h}}$ (lower left), and 4${\tau _\mathrm {h}}$ (lower right) categories. The SM HH signal is shown for a cross section amounting to 30 times the value predicted in the SM. The distributions expected for the background processes are shown for the values of nuisance parameters obtained from the ML fit of the signal+background hypothesis to the data. |
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Figure 8-b:
Distribution in the output of the BDT trained for nonresonant HH production and evaluated for the benchmark scenario JHEP04 BM7 for the 3${\ell}$+1${\tau _\mathrm {h}}$ (upper left), 2${\ell}$+2${\tau _\mathrm {h}}$ (upper right), 1${\ell}$+3${\tau _\mathrm {h}}$ (lower left), and 4${\tau _\mathrm {h}}$ (lower right) categories. The SM HH signal is shown for a cross section amounting to 30 times the value predicted in the SM. The distributions expected for the background processes are shown for the values of nuisance parameters obtained from the ML fit of the signal+background hypothesis to the data. |
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Figure 8-c:
Distribution in the output of the BDT trained for nonresonant HH production and evaluated for the benchmark scenario JHEP04 BM7 for the 3${\ell}$+1${\tau _\mathrm {h}}$ (upper left), 2${\ell}$+2${\tau _\mathrm {h}}$ (upper right), 1${\ell}$+3${\tau _\mathrm {h}}$ (lower left), and 4${\tau _\mathrm {h}}$ (lower right) categories. The SM HH signal is shown for a cross section amounting to 30 times the value predicted in the SM. The distributions expected for the background processes are shown for the values of nuisance parameters obtained from the ML fit of the signal+background hypothesis to the data. |
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Figure 8-d:
Distribution in the output of the BDT trained for nonresonant HH production and evaluated for the benchmark scenario JHEP04 BM7 for the 3${\ell}$+1${\tau _\mathrm {h}}$ (upper left), 2${\ell}$+2${\tau _\mathrm {h}}$ (upper right), 1${\ell}$+3${\tau _\mathrm {h}}$ (lower left), and 4${\tau _\mathrm {h}}$ (lower right) categories. The SM HH signal is shown for a cross section amounting to 30 times the value predicted in the SM. The distributions expected for the background processes are shown for the values of nuisance parameters obtained from the ML fit of the signal+background hypothesis to the data. |
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Figure 9:
Observed and expected 95% CL upper limits on the SM HH production cross section, obtained for both individual search categories and from a simultaneous fit of all seven categories combined. |
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Figure 10:
Observed and expected 95% CL upper limits on the HH production cross section as a function of the H boson self-coupling strength modifier ${\kappa _{\lambda}}$. All H boson couplings other than $\lambda $ are assumed to have the values predicted in the SM. The left plot shows the result obtained by combining all seven search categories, while the right plot shows the limits obtained for each category separately. The red curve in the left plot represents the SM prediction for the HH production cross section as a function of ${\kappa _{\lambda}}$ , and the red shaded band the theoretical uncertainty in this prediction. |
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Figure 10-a:
Observed and expected 95% CL upper limits on the HH production cross section as a function of the H boson self-coupling strength modifier ${\kappa _{\lambda}}$. All H boson couplings other than $\lambda $ are assumed to have the values predicted in the SM. The left plot shows the result obtained by combining all seven search categories, while the right plot shows the limits obtained for each category separately. The red curve in the left plot represents the SM prediction for the HH production cross section as a function of ${\kappa _{\lambda}}$ , and the red shaded band the theoretical uncertainty in this prediction. |
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Figure 10-b:
Observed and expected 95% CL upper limits on the HH production cross section as a function of the H boson self-coupling strength modifier ${\kappa _{\lambda}}$. All H boson couplings other than $\lambda $ are assumed to have the values predicted in the SM. The left plot shows the result obtained by combining all seven search categories, while the right plot shows the limits obtained for each category separately. The red curve in the left plot represents the SM prediction for the HH production cross section as a function of ${\kappa _{\lambda}}$ , and the red shaded band the theoretical uncertainty in this prediction. |
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Figure 11:
Observed and expected 95% CL upper limits on the HH production cross section for the twelve benchmark scenarios from Ref. [24], the additional benchmark scenario 8a from Ref. [59], the seven benchmark scenarios from Ref. [58], and for the SM. The upper plot shows the result obtained by combining all seven search categories, while the lower plot shows the limits obtained for each category separately, and the combined limit. |
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Figure 11-a:
Observed and expected 95% CL upper limits on the HH production cross section for the twelve benchmark scenarios from Ref. [24], the additional benchmark scenario 8a from Ref. [59], the seven benchmark scenarios from Ref. [58], and for the SM. The upper plot shows the result obtained by combining all seven search categories, while the lower plot shows the limits obtained for each category separately, and the combined limit. |
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Figure 11-b:
Observed and expected 95% CL upper limits on the HH production cross section for the twelve benchmark scenarios from Ref. [24], the additional benchmark scenario 8a from Ref. [59], the seven benchmark scenarios from Ref. [58], and for the SM. The upper plot shows the result obtained by combining all seven search categories, while the lower plot shows the limits obtained for each category separately, and the combined limit. |
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Figure 12:
Observed and expected limits on the HH production cross section as a function of the effective coupling ${\text {c}_{2}}$ (left), and the region excluded in the ${\kappa _{{\mathrm{t}}}} - {\text {c}_{2}}$ plane (right). All limits are computed at 95% CL. H boson couplings other than the ones shown in the plots (${\text {c}_{2}}$ in the left plot and ${\text {c}_{2}}$ and ${\kappa _{{\mathrm{t}}}}$ in the right plot) are assumed to have the values predicted by the SM. |
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Figure 12-a:
Observed and expected limits on the HH production cross section as a function of the effective coupling ${\text {c}_{2}}$ (left), and the region excluded in the ${\kappa _{{\mathrm{t}}}} - {\text {c}_{2}}$ plane (right). All limits are computed at 95% CL. H boson couplings other than the ones shown in the plots (${\text {c}_{2}}$ in the left plot and ${\text {c}_{2}}$ and ${\kappa _{{\mathrm{t}}}}$ in the right plot) are assumed to have the values predicted by the SM. |
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Figure 12-b:
Observed and expected limits on the HH production cross section as a function of the effective coupling ${\text {c}_{2}}$ (left), and the region excluded in the ${\kappa _{{\mathrm{t}}}} - {\text {c}_{2}}$ plane (right). All limits are computed at 95% CL. H boson couplings other than the ones shown in the plots (${\text {c}_{2}}$ in the left plot and ${\text {c}_{2}}$ and ${\kappa _{{\mathrm{t}}}}$ in the right plot) are assumed to have the values predicted by the SM. |
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Figure 13:
Observed and expected regions excluded in the $ \kappa_{\mathrm{t}} $-$ \kappa_{\lambda} $ (left) and $ \kappa_{\lambda} $-$ \text{c}_{2} $ (right) planes. H boson couplings other than the ones shown in the plots ($ \kappa_{\lambda} $ and $ \kappa_{\mathrm{t}} $ in the left plot, and $ \text{c}_{2} $ and $ \kappa_{\lambda} $ in the right plot) are assumed to have the values predicted by the SM. |
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Figure 13-a:
Observed and expected regions excluded in the $ \kappa_{\mathrm{t}} $-$ \kappa_{\lambda} $ (left) and $ \kappa_{\lambda} $-$ \text{c}_{2} $ (right) planes. H boson couplings other than the ones shown in the plots ($ \kappa_{\lambda} $ and $ \kappa_{\mathrm{t}} $ in the left plot, and $ \text{c}_{2} $ and $ \kappa_{\lambda} $ in the right plot) are assumed to have the values predicted by the SM. |
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Figure 13-b:
Observed and expected regions excluded in the $ \kappa_{\mathrm{t}} $-$ \kappa_{\lambda} $ (left) and $ \kappa_{\lambda} $-$ \text{c}_{2} $ (right) planes. H boson couplings other than the ones shown in the plots ($ \kappa_{\lambda} $ and $ \kappa_{\mathrm{t}} $ in the left plot, and $ \text{c}_{2} $ and $ \kappa_{\lambda} $ in the right plot) are assumed to have the values predicted by the SM. |
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Figure 14:
Observed and expected 95% CL upper limits on the production of new particles X of spin 0 (upper) and spin 2 (lower) and mass $m_{{\textrm {X}}}$ in the range 250-1000 GeV, which decay to H boson pairs. The plot on the left shows the result obtained by combining all seven search categories, while the plot on the right shows the limits obtained for each category separately, and the combined limit. |
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Figure 14-a:
Observed and expected 95% CL upper limits on the production of new particles X of spin 0 (upper) and spin 2 (lower) and mass $m_{{\textrm {X}}}$ in the range 250-1000 GeV, which decay to H boson pairs. The plot on the left shows the result obtained by combining all seven search categories, while the plot on the right shows the limits obtained for each category separately, and the combined limit. |
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Figure 14-b:
Observed and expected 95% CL upper limits on the production of new particles X of spin 0 (upper) and spin 2 (lower) and mass $m_{{\textrm {X}}}$ in the range 250-1000 GeV, which decay to H boson pairs. The plot on the left shows the result obtained by combining all seven search categories, while the plot on the right shows the limits obtained for each category separately, and the combined limit. |
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Figure 14-c:
Observed and expected 95% CL upper limits on the production of new particles X of spin 0 (upper) and spin 2 (lower) and mass $m_{{\textrm {X}}}$ in the range 250-1000 GeV, which decay to H boson pairs. The plot on the left shows the result obtained by combining all seven search categories, while the plot on the right shows the limits obtained for each category separately, and the combined limit. |
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Figure 14-d:
Observed and expected 95% CL upper limits on the production of new particles X of spin 0 (upper) and spin 2 (lower) and mass $m_{{\textrm {X}}}$ in the range 250-1000 GeV, which decay to H boson pairs. The plot on the left shows the result obtained by combining all seven search categories, while the plot on the right shows the limits obtained for each category separately, and the combined limit. |
| Tables | |
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Table 1:
Selection requirements on $ p_{\mathrm{T}} $ and $ \eta $ of reconstructed electrons (e), muons ($ \mu $), and hadronically decaying tau leptons ($ \tau_\mathrm{h} $) applied by the triggers used in this analysis. The trigger $ p_{\mathrm{T}} $ thresholds for leading, subleading, and third e, $ \mu $, or $ \tau_\mathrm{h} $ are separated by commas. For trigger thresholds that varied over time, the range of variation is indicated. |
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Table 2:
The MC generators that are used to simulate HH signal and background processes. The order of MC simulation and cross section calculation both refer to the perturbative expansion in QCD. Additional higher order electroweak (EW) corrections, if present, are indicated separately. |
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Table 3:
Parameter values for $ \kappa_{\lambda} $, $ \kappa_{\mathrm{t}} $, $ \text{c}_{2} $, $ \text{c}_{\mathrm{g}} $, and $ \text{c}_{2\mathrm{g}} $ in MC samples modeling twenty benchmark scenarios in the EFT approach, plus SM HH production. |
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Table 4:
Event selection criteria applied in the seven search categories. The $ p_{\mathrm{T}} $ thresholds for $ \ell $ and $ \tau_\mathrm{h} $ with the highest, second-, third-, and fourth-highest $ p_{\mathrm{T}} $ are separated by slashes. The symbol ``$ \text{---} $'' indicates that no requirement is applied. |
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Table 5:
Reconstructed object and event selection requirements in all seven search categories. Electrons or muons in the $ \ell\ell $ pairs include any leptons passing the loose selection criteria. |
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Table 6:
The number of expected and observed events in each of the seven search categories, and in two CRs, which validate the modeling of the WZ and ZZ backgrounds. The symbol ``$ \text{---} $'' indicates that the background is not relevant for the category. The HH signal represents the sum of the $ \mathrm{g}\mathrm{g}\mathrm{H}\mathrm{H} $ and $ \mathrm{q}\mathrm{q}\mathrm{H}\mathrm{H} $ production processes and is normalized to 30 times the event yield expected in the SM, corresponding to a cross section of about 1$ \,\text{pb} $. The event yields are obtained by performing the event selection and applying appropriate corrections to the simulated events. Quoted uncertainties represent the sum of statistical and systematic components. Uncertainties that are smaller than half the value of the least significant digit have been rounded to zero. |
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Table 7:
The number of expected and observed events in each of the seven search categories, and in two CRs, which validate the modeling of the WZ and ZZ backgrounds. The $ \ell $/$ \tau_\mathrm{h} $ misidentification and electron charge misidentification backgrounds are determined from data, as described in Section 7, while the HH signal and all other backgrounds are modeled using MC simulation. The symbol ``$ \text{---} $'' indicates that the background is not relevant for the category. The HH signal represents the sum of the $ \mathrm{g}\mathrm{g}\mathrm{H}\mathrm{H} $ and $ \mathrm{q}\mathrm{q}\mathrm{H}\mathrm{H} $ production processes and is normalized to 30 times the event yield expected in the SM, corresponding to a cross section of about 1$ \,\text{pb} $. The expected event yields are computed for the values of nuisance parameters obtained from the ML fit described in Section 9. Quoted uncertainties represent the sum of statistical and systematic components. Uncertainties that are smaller than half the value of the least significant digit have been rounded to zero. |
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Table 8:
Observed (expected) 95% CL upper limits on the $ \mathrm{g}\mathrm{g}\mathrm{H}\mathrm{H} $ production cross section for the twelve benchmark scenarios from Ref. [24], the additional benchmark scenario 8a from Ref. [97] and the seven benchmark scenarios from Ref. [96]. The corresponding observed (expected) upper limit for the SM is 652 (583)$ \,\text{fb} $. The limits correspond to the combination of all seven search categories. |
| Summary |
| The results of a search for nonresonant as well as resonant Higgs boson pair (HH) production in final states with multiple reconstructed leptons, including electrons and muons (${\ell} $) as well as hadronically decaying tau leptons (${\tau_\mathrm{h}}$), has been presented. The search targets the HH decay modes WWWW, WW$\tau\tau$, and $\tau\tau\tau\tau$, using proton-proton collision data recorded by the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb$^{-1}$. Seven search categories, distinguished by ${\ell}$ and ${\tau_\mathrm{h}}$ multiplicity, are included in the analysis: 2$\ell$ss, 3$\ell$, 4$\ell$, 3$\ell$+1${\tau_\mathrm{h}}$, 2$\ell$+2${\tau_\mathrm{h}}$, 1$\ell$+3${\tau_\mathrm{h}}$, and 4${\tau_\mathrm{h}}$, where "ss'' indicates an $\ell\ell$ pair with the same charge. No evidence for a signal is found in the data. Upper limits on the cross section for nonresonant as well as resonant HH production are set. The observed (expected) limits on the nonresonant HH production cross section in twenty EFT benchmark scenarios range from 0.21 to 1.09 (0.16 to 1.16) pb at 95% confidence level (CL), depending on the scenario. For nonresonant HH production with event kinematics as predicted by the standard model (SM), the observed (expected) 95% CL upper limit on the HH production rate is 21.3 (19.4) times the rate expected in the SM. The results of the search for nonresonant HH production are used to exclude regions in the plane of the H boson coupling to the top quark, ${\text{y}_{{\mathrm{t}} }}$, and of the trilinear Higgs boson self-coupling, $\lambda$. Assuming ${\text{y}_{{\mathrm{t}} }}$ has the value expected in the SM, the observed (expected) 95% CL interval for $\lambda$ is between $-$6.9 and 11.1 ($-$6.9 and 11.7) times the value expected in the SM. The resonant production of H boson pairs, resulting from decays of new heavy particles X with mass $m_{{\textrm{X}} }$, is probed within the mass range 250-1000 GeV. The corresponding observed (expected) 95% CL upper limits on the cross section for resonant HH production range from 0.18 to 0.90 (0.08 to 1.06) pb, depending on the mass and spin of the resonance. |
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