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CMS-PAS-HIG-16-024
Search for Higgs boson pair production in the $\mathrm{b}\overline{\mathrm{b}} \ell\nu \ell\nu$ final state at $ \sqrt{s} = $ 13 TeV
Abstract: A search for pair-produced Higgs bosons decaying respectively into $\mathrm{b}\overline{\mathrm{b}}$ and VV (with V either a W or a Z boson), with subsequent VV decays into two leptons and two neutrinos, is presented. The analysis is based on a sample of proton-proton collisions at $ \sqrt{s} = $ 13 TeV at the LHC corresponding to an integrated luminosity of 2.30 fb$^{-1}$. The search signature is a resonance in the invariant mass distribution of the b-jet pair at the Higgs boson mass in combination with high scores of a boosted decision tree discriminant based on kinematic information. Data and predictions from the standard model (SM) are in agreement within uncertainties. For the SM hh hypothesis, the data are observed (expected) to exclude a production cross-section times branching ratio of 166.7 (92.8$^{+59.9}_{-33.4}$) fb, corresponding to approximately 400 times the SM cross section. Lack of deviation from the SM predictions in the observations is used to place constraints on different scenarios considering anomalous couplings which could affect the rate and kinematics of hh production.
Figures & Tables Summary Additional Figures & Material References CMS Publications
Figures

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Figure 1-a:
Higgs pair production diagrams via gluon fusion for both SM (a,b,c) and BSM (d,e).

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Figure 1-b:
Higgs pair production diagrams via gluon fusion for both SM (a,b,c) and BSM (d,e).

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Figure 1-c:
Higgs pair production diagrams via gluon fusion for both SM (a,b,c) and BSM (d,e).

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Figure 1-d:
Higgs pair production diagrams via gluon fusion for both SM (a,b,c) and BSM (d,e).

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Figure 1-e:
Higgs pair production diagrams via gluon fusion for both SM (a,b,c) and BSM (d,e).

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Figure 2-a:
The $ {p_{\mathrm {T}}} ^{ {\ell} {\ell} }$ (a) and $ {p_{\mathrm {T}}} ^{ {\mathrm {j}} {\mathrm {j}} }$ (b) distributions for data and simulated events after requiring two leptons, two b-tagged jets, and $ {\mathrm {m}_{ {\ell} {\ell} }} < \rm {m}_{ {\mathrm {Z}} } - 15$GeV, for all dilepton channels ($ {\mathrm {e}} {\mathrm {e}}$, $ {\mathrm {e}} {\mu } $, $ {\mu } {\mathrm {e}}$ and $ {\mu } {\mu } $). Four BMs along with the SM signal are shown as solid lines. The signal cross-sections times branching fraction are arbitrarily normalized to 5pb for display purposes. Hashed area corresponds to postfit uncertainties, as described in section 6.

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Figure 2-b:
The $ {p_{\mathrm {T}}} ^{ {\ell} {\ell} }$ (a) and $ {p_{\mathrm {T}}} ^{ {\mathrm {j}} {\mathrm {j}} }$ (b) distributions for data and simulated events after requiring two leptons, two b-tagged jets, and $ {\mathrm {m}_{ {\ell} {\ell} }} < \rm {m}_{ {\mathrm {Z}} } - 15$GeV, for all dilepton channels ($ {\mathrm {e}} {\mathrm {e}}$, $ {\mathrm {e}} {\mu } $, $ {\mu } {\mathrm {e}}$ and $ {\mu } {\mu } $). Four BMs along with the SM signal are shown as solid lines. The signal cross-sections times branching fraction are arbitrarily normalized to 5pb for display purposes. Hashed area corresponds to postfit uncertainties, as described in section 6.

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Figure 3-a:
The BDT output (a) and ${\mathrm {m}_{ {\mathrm {j}} {\mathrm {j}} }}$ (b) distributions for data and simulated events for all dilepton channels ($ {\mathrm {e}} {\mathrm {e}}$, $ {\mathrm {e}} {\mu } $, $ {\mu } {\mathrm {e}}$ and $ {\mu } {\mu } $) after requiring all selection cuts. Four BMs along with the SM signal are shown as solid lines. The signal cross-sections times branching fraction are arbitrarily normalized to 5 pb. Hashed area corresponds to postfit uncertainties, as described in section 6.

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Figure 3-b:
The BDT output (a) and ${\mathrm {m}_{ {\mathrm {j}} {\mathrm {j}} }}$ (b) distributions for data and simulated events for all dilepton channels ($ {\mathrm {e}} {\mathrm {e}}$, $ {\mathrm {e}} {\mu } $, $ {\mu } {\mathrm {e}}$ and $ {\mu } {\mu } $) after requiring all selection cuts. Four BMs along with the SM signal are shown as solid lines. The signal cross-sections times branching fraction are arbitrarily normalized to 5 pb. Hashed area corresponds to postfit uncertainties, as described in section 6.

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Figure 4:
BDT output distribution for data and simulated events for all dilepton channels ($ {\mathrm {e}} {\mathrm {e}}$, $ {\mathrm {e}} {\mu } $, $ {\mu } {\mathrm {e}}$ and $ {\mu } {\mu } $) in three different ${\mathrm {m}_{ {\mathrm {j}} {\mathrm {j}} }}$ regions: $ {\mathrm {m}_{ {\mathrm {j}} {\mathrm {j}} }} < $ 75 GeV (a), $ {\mathrm {m}_{ {\mathrm {j}} {\mathrm {j}} }} \in $ [75, 140[ GeV (b) and $ {\mathrm {m}_{ {\mathrm {j}} {\mathrm {j}} }} \geq $ 140 GeV (c). Four BMs along with the SM signal are shown as solid lines. The signal cross-sections times branching fraction are arbitrarily normalized to 5pb. Hashed area corresponds to postfit uncertainties, as described in section 6.

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Figure 5-a:
Expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction for $ {\mathrm {h}} {\mathrm {h}} \to { {\mathrm {b}} {\overline {\mathrm {b}}} } {\mathrm {V}} {\mathrm {V}} \to { {\mathrm {b}} {\overline {\mathrm {b}}} } {\ell} {\nu } {\ell} {\nu } $ as a function of $\kappa _{\lambda }$ (top) and $\kappa _{t}$ (bottom). The $\kappa _{\lambda }$ ($\kappa _{t}$) scans are performed assuming $c_{2} =0$, $c_{g} = 0$, and $c_{2g} = 0$, while $\kappa _{t} = 1$ ($\kappa _{\lambda } =1$). These limits are computed using the asymptotic CL$_s$ method. Theory predictions are extracted from [9,10,11,12,13,14,54].

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Figure 5-b:
Expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction for $ {\mathrm {h}} {\mathrm {h}} \to { {\mathrm {b}} {\overline {\mathrm {b}}} } {\mathrm {V}} {\mathrm {V}} \to { {\mathrm {b}} {\overline {\mathrm {b}}} } {\ell} {\nu } {\ell} {\nu } $ as a function of $\kappa _{\lambda }$ (top) and $\kappa _{t}$ (bottom). The $\kappa _{\lambda }$ ($\kappa _{t}$) scans are performed assuming $c_{2} =0$, $c_{g} = 0$, and $c_{2g} = 0$, while $\kappa _{t} = 1$ ($\kappa _{\lambda } =1$). These limits are computed using the asymptotic CL$_s$ method. Theory predictions are extracted from [9,10,11,12,13,14,54].

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Figure 6-a:
Allowed (empty half-circles) and excluded (solid half-circles) points of the BSM parameter space at expected and observed 95% CL in the $\kappa _{\lambda }$ vs $\kappa _{t}$ plane. Theoretical cross-section times branching fraction isolines for $ {\mathrm {h}} {\mathrm {h}} \to { {\mathrm {b}} {\overline {\mathrm {b}}} } {\mathrm {V}} {\mathrm {V}} \to { {\mathrm {b}} {\overline {\mathrm {b}}} } {\ell} {\nu } {\ell} {\nu } $ are shown as dashed lines. Other BSM couplings are set to their (null) SM value in the upper figure, and to $c_{2} =-3$, $c_{g} = 0$, and $c_{2g} = 0$ in the bottom figure. The limits are computed using the asymptotic CL$_s$ method. Theory predictions are extracted from [9,10,11,12,13,14,54].

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Figure 6-b:
Allowed (empty half-circles) and excluded (solid half-circles) points of the BSM parameter space at expected and observed 95% CL in the $\kappa _{\lambda }$ vs $\kappa _{t}$ plane. Theoretical cross-section times branching fraction isolines for $ {\mathrm {h}} {\mathrm {h}} \to { {\mathrm {b}} {\overline {\mathrm {b}}} } {\mathrm {V}} {\mathrm {V}} \to { {\mathrm {b}} {\overline {\mathrm {b}}} } {\ell} {\nu } {\ell} {\nu } $ are shown as dashed lines. Other BSM couplings are set to their (null) SM value in the upper figure, and to $c_{2} =-3$, $c_{g} = 0$, and $c_{2g} = 0$ in the bottom figure. The limits are computed using the asymptotic CL$_s$ method. Theory predictions are extracted from [9,10,11,12,13,14,54].
Tables

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Table 1:
Summary of the systematic uncertainties and their impact range on total background yields and on the SM signal in the final region.
Summary
We have presented a search for Higgs boson pair production, hh, where one of the h decays as $\mathrm{h} \to \mathrm{ b \bar{b} }$, and the other as $\mathrm{h} \to \mathrm{V}\mathrm{V} \to \ell\nu \ell\nu$, using LHC proton-proton collision data at $\sqrt{s} =$ 13 TeV corresponding to an integrated luminosity of 2.30 fb$^{-1}$. Data and standard model predictions are in agreement within uncertainties. For the SM hh hypothesis, the data are observed (expected) to exclude a production cross section times branching ratio of 166.7 (92.8$^{+59.9}_{-33.4}$) fb, corresponding to approximately 400 times the SM cross section. Searching for deviations from the SM, upper limits are set on $\mathrm{h}\mathrm{h} \to \mathrm{ b \bar{b} }\mathrm{V}\mathrm{V} \to \mathrm{ b \bar{b} }\ell\nu\ell\nu$ cross section in scenarios considering five anomalous couplings: $\kappa_{\lambda}$, $\kappa_{t}$, $c_{2}$, $c_{g}$, and $c_{2g}$. The search for Higgs boson pair production in the $\mathrm{ b \bar{b} }\ell\nu\ell\nu$ final state is performed for the first time using LHC data. With the present luminosity, the analysis is insensitive to SM hh production but is already excluding some regions of the BSM parameter space.
Additional Figures

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Additional Figure 1:
Expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction for $\mathrm{h} \mathrm{h} \to {\mathrm{ b \bar{b} } } \mathrm {V}\mathrm {V} \to {\mathrm{ b \bar{b} } } \ell \nu \ell \nu $ as a function of $\kappa _{\lambda }$. The scan is performed assuming $\kappa _{\mathrm{ t } } = 1.5, c_{2} = -2$, $c_{\mathrm{g} } = 0$, and $c_{2\mathrm{g} } = 0$, These limits are computed using the asymptotic CL$_s$ method.

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Additional Figure 2:
Expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction for $\mathrm{h} \mathrm{h} \to {\mathrm{ b \bar{b} } } \mathrm {V}\mathrm {V} \to {\mathrm{ b \bar{b} } } \ell \nu \ell \nu $ as a function of $c_{2}$. The scan is performed assuming $\kappa _{\lambda } = 1, \kappa _{\mathrm{ t } } = 1, c_{\mathrm{g} } = 0$, and $c_{2\mathrm{g} } = 0$, These limits are computed using the asymptotic CL$_s$ method.

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Additional Figure 3:
Expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction for $\mathrm{h} \mathrm{h} \to {\mathrm{ b \bar{b} } } \mathrm {V}\mathrm {V} \to {\mathrm{ b \bar{b} } } \ell \nu \ell \nu $ as a function of $c_{\mathrm{g} }$. The scan is performed assuming $\kappa _{\lambda } = 1, \kappa _{\mathrm{ t } } = 1, c_{2} = 0$, and $c_{2\mathrm{g} } = 0$, These limits are computed using the asymptotic CL$_s$ method.

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Additional Figure 4:
Expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction for $\mathrm{h} \mathrm{h} \to {\mathrm{ b \bar{b} } } \mathrm {V}\mathrm {V} \to {\mathrm{ b \bar{b} } } \ell \nu \ell \nu $ as a function of $c_{2\mathrm{g} }$. The scan is performed assuming $\kappa _{\lambda } = 1, \kappa _{\mathrm{ t } } = 1, c_{2} = 0$, and $c_{\mathrm{g} } = 0$, These limits are computed using the asymptotic CL$_s$ method.

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Additional Figure 5:
Expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction for $\mathrm{h} \mathrm{h} \to {\mathrm{ b \bar{b} } } \mathrm {V}\mathrm {V} \to {\mathrm{ b \bar{b} } } \ell \nu \ell \nu $ for each benchmark of the analysis, in addition to the SM case. These limits are computed using the asymptotic CL$_s$ method.

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Additional Figure 6:
Expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction for $\mathrm{h} \mathrm{h} \to {\mathrm{ b \bar{b} } } \mathrm {V}\mathrm {V} \to {\mathrm{ b \bar{b} } } \ell \nu \ell \nu $ for each benchmark of the analysis, in addition to the SM case. These limits are computed using the asymptotic CL$_s$ method.
Additional Material
Complete set of results for expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction

The complete set of results consist of the experimental observations for all 1459 points of the parameter space that were studied.

The results are available both in JSON and CSV format. The results files consist of the following quantities:

  • Value of the coupling modifier of the Higgs boson self coupling $\kappa_\lambda$, denoted in the files as kappa_lambda
  • Value of the coupling modifier of the top quark Yukawa coupling $\kappa_{\rm{t}}$, denoted in the files as kappa_top
  • Value of the coupling of the contact-like interaction of the Higgs boson with gluons $c_{\rm{g}}$, denoted in the files as cg
  • Value of the coupling of the contact-like interaction of the Higgs boson pair with a gluon pair $c_{2\rm{g}}$, denoted in the files as c2g
  • Value of the coupling of the contact-like interaction of the Higgs boson pair with a top quark pair $c_{2}$, denoted in the files as c2
  • Observed 95% CL upper limit on the cross-section times branching fraction (in fb), denoted in the files as limit_observed
  • Expected 95% CL upper limit on the cross-section times branching fraction (in fb), denoted in the files as limit_expected
  • Variation of the expected 95% CL upper limit on the cross-section times branching fraction of $\pm 1$ standard deviation, denoted in the JSON file as limit_expected_one_sigma and in the CSV file as limit_expected_one_sigma_up and limit_expected_one_sigma_down. Note: the first entry on the array is the $-1\sigma$ variated value
  • Variation of the expected 95% CL upper limit on the cross-section times branching fraction of $\pm 2$ standard deviation, denoted in the JSON file as limit_expected_two_sigma and in the CSV file as limit_expected_two_sigma_up and limit_expected_two_sigma_down. Note: the first entry on the array is the $-2\sigma$ variated value
  • Theory prediction on the cross-section times branching fraction (in fb), denoted in the files as cross_section
  • Variation of the theory prediction on the cross-section times branching fraction of $\pm 1$ standard deviation, denoted in the JSON file as cross_section_one_sigma and in the CSV file as cross_section_one_sigma_up and cross_section_one_sigma_down. Note: the first entry on the array is the $-1\sigma$ variation

Note that:

  • all upper limits are in fb and on the Higgs pair production cross section times branching fraction for $\rm{hh}\to\rm{b}\bar{\rm{b}}\rm{VV}\to\rm{b}\bar{\rm{b}}\rm{l}\nu\rm{l}\nu$. Both $\rm{Z}$ and $\rm{W}$ bosons are considered in their proportions as predicted by the Standard Model. Only electrons and muons are considered as leptons, while all three neutrino flavours are considered.
  • The theory predictions are taken from JHEP 1604 (2016) 126, and are multiplied by the branching fraction, described above, of 1.23%

Please find below an excerpt of the file in JSON format:
  [
  {
    "cg": 0.0,
    "limit_expected_two_sigma": [
    55.72,
    322.45
    ],
    "c2": 0.5,
    "cross_section": 1386.6,
    "cross_section_one_sigma": [
    1270.01,
    1487.72
    ],
    "kappa_lambda": 1.0,
    "limit_observed": 212.7,
    "kappa_top": 2.5,
    "c2g": 0.0,
    "limit_expected": 123.5,
    "limit_expected_one_sigma": [
    79.81,
    201.28
    ]
  },
  (...)
  ]
        
Please find below an excerpt of the file in CSV format:
	  kappa_lambda    kappa_top   c2  cg  c2g cross_section   cross_section_one_sigma_down    cross_section_one_sigma_up  limit_expected  limit_observed  
	  limit_expected_one_sigma_down   limit_expected_one_sigma_up limit_expected_two_sigma_down   limit_expected_two_sigma_up
	  1.0 2.5 0.5 0.0 0.0 1386.6  1270.01 1487.72 123.5   212.7   79.81   201.28  55.72   322.45
        

Results

Complete set of results for expected and observed 95% CL upper limits on the Higgs pair production cross section times branching fraction

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