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CMS-HIG-17-008 ; CERN-EP-2017-343
Search for Higgs boson pair production in the $\gamma\gamma\mathrm{b\bar{b}}$ final state in pp collisions at $\sqrt{s} = $ 13 TeV
Phys. Lett. B 788 (2018) 7
Abstract: A search is presented for the production of a pair of Higgs bosons, where one decays into two photons and the other one into a bottom quark-antiquark pair. The analysis is performed using proton-proton collision data at $\sqrt{s} = $ 13 TeV recorded in 2016 by the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The results are in agreement with standard model (SM) predictions. In a search for resonant production, upper limits are set on the cross section for new spin-0 or spin-2 particles. For the SM-like nonresonant production hypothesis, the data exclude a product of cross section and branching fraction larger than 2.0 fb at 95% confidence level (CL), corresponding to about 24 times the SM prediction. Values of the effective Higgs boson self-coupling $\kappa_\lambda$ are constrained to be within the range $-11 < \kappa_\lambda < 17$ at 95% CL, assuming all other Higgs boson couplings are at their SM value. These constraints are the most restrictive to date.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Feynman diagrams that contribute to ggHH at LO. Top diagrams correspond to SM-like processes, referred to as box and triangle diagrams, respectively, while bottom diagrams correspond to pure BSM effects: the first exploits the contact interaction of two Higgs bosons with two top quarks and the last two describe contact interactions between the H boson and gluons.

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Figure 1-a:
Feynman diagram that contributes to ggHH at LO. It corresponds to a SM-like process referred to as triangle diagram.

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Figure 1-b:
Feynman diagram that contributes to ggHH at LO. It corresponds to a SM-like process,referred to as box diagram.

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Figure 1-c:
Feynman diagram that contributes to ggHH at LO. It corresponds to a pure BSM effect involving the contact interaction of two Higgs bosons with two top quarks.

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Figure 1-d:
Feynman diagram that contributes to ggHH at LO. It corresponds to a pure BSM effect involving the contact interaction of two Higgs bosons with two gluons.

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Figure 1-e:
Feynman diagram that contributes to ggHH at LO. It corresponds to a pure BSM effect involving the contact interaction of two Higgs bosons with one gluon.

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Figure 2:
Comparison of $ {\tilde{M}_{\mathrm {X}}} $ (red line) with $ {m_{\gamma \gamma \text {jj}}}$ (purple dotted line) for different spin-2 resonance masses. All distributions are obtained after the full baseline selection (Table 2), and are normalized to unit area.

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Figure 3:
Data (dots), dominated by n$\gamma$+jets background, compared to different signal hypotheses and three single-Higgs boson samples (ttH, VH, and ggH) after the selections on photons and jets summarized in Table 2 for the kinematic distributions described in Sections 1 and 4.3: $ {\tilde{M}_{\mathrm {X}}} $ (top left) and $ | \cos{\theta ^\text {CS}_{{{{\mathrm {H}} {\mathrm {H}}}}}} |$ (top right); $ {m_{\gamma \gamma}} $ (middle left) and $ | \cos{\theta _{\gamma \gamma}} |$ (middle right); $ {m_\text {jj}}$ (bottom left) and $ | \cos{\theta _\text {jj}} | $ (bottom right). The statistical uncertainties on data are barely visible beyond the markers. The resonant signal cross section is normalized to 500 fb.

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Figure 3-a:
Data (dots), dominated by n$\gamma$+jets background, compared to different signal hypotheses and three single-Higgs boson samples (ttH, VH, and ggH) after the selections on photons and jets summarized in Table 2 for the kinematic distributions described in Sections 1 and 4.3: $ {\tilde{M}_{\mathrm {X}}} $. The statistical uncertainties on data are barely visible beyond the markers. The resonant signal cross section is normalized to 500 fb.

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Figure 3-b:
Data (dots), dominated by n$\gamma$+jets background, compared to different signal hypotheses and three single-Higgs boson samples (ttH, VH, and ggH) after the selections on photons and jets summarized in Table 2 for the kinematic distributions described in Sections 1 and 4.3: $ | \cos{\theta ^\text {CS}_{{{{\mathrm {H}} {\mathrm {H}}}}}} |$. The statistical uncertainties on data are barely visible beyond the markers. The resonant signal cross section is normalized to 500 fb.

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Figure 3-c:
Data (dots), dominated by n$\gamma$+jets background, compared to different signal hypotheses and three single-Higgs boson samples (ttH, VH, and ggH) after the selections on photons and jets summarized in Table 2 for the kinematic distributions described in Sections 1 and 4.3: $ {m_{\gamma \gamma}} $. The statistical uncertainties on data are barely visible beyond the markers. The resonant signal cross section is normalized to 500 fb.

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Figure 3-d:
Data (dots), dominated by n$\gamma$+jets background, compared to different signal hypotheses and three single-Higgs boson samples (ttH, VH, and ggH) after the selections on photons and jets summarized in Table 2 for the kinematic distributions described in Sections 1 and 4.3: $ | \cos{\theta _{\gamma \gamma}} |$. The statistical uncertainties on data are barely visible beyond the markers. The resonant signal cross section is normalized to 500 fb.

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Figure 3-e:
Data (dots), dominated by n$\gamma$+jets background, compared to different signal hypotheses and three single-Higgs boson samples (ttH, VH, and ggH) after the selections on photons and jets summarized in Table 2 for the kinematic distributions described in Sections 1 and 4.3: $ {m_\text {jj}}$. The statistical uncertainties on data are barely visible beyond the markers. The resonant signal cross section is normalized to 500 fb.

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Figure 3-f:
Data (dots), dominated by n$\gamma$+jets background, compared to different signal hypotheses and three single-Higgs boson samples (ttH, VH, and ggH) after the selections on photons and jets summarized in Table 2 for the kinematic distributions described in Sections 1 and 4.3: $ | \cos{\theta _\text {jj}} | $. The statistical uncertainties on data are barely visible beyond the markers. The resonant signal cross section is normalized to 500 fb.

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Figure 4:
Distributions of the BDT output (classification MVA) obtained for the high-mass nonresonant training. Data, dominated by n$\gamma$+jets background, are compared to different signal hypotheses and three single-Higgs boson samples (ttH, VH, and ggH) after the selections on photons and jets summarized in Table 2.The resonant signal cross section is normalised to 500 fb.

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Figure 5:
Consecutive selection efficiencies for different analysis steps for two resonance hypotheses: spin-0 (left) and spin-2 (right). Online selection includes the photon online preselection conditions described at the beginning of Section 4. Diphoton selections include photon identification and kinematics selections from Table 2. Dijet selections are those described in Table 2.

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Figure 5-a:
Consecutive selection efficiencies for different analysis steps for two resonance hypotheses: spin-0. Online selection includes the photon online preselection conditions described at the beginning of Section 4. Diphoton selections include photon identification and kinematics selections from Table 2. Dijet selections are those described in Table 2.

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Figure 5-b:
Consecutive selection efficiencies for different analysis steps for two resonance hypotheses: spin-2. Online selection includes the photon online preselection conditions described at the beginning of Section 4. Diphoton selections include photon identification and kinematics selections from Table 2. Dijet selections are those described in Table 2.

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Figure 6:
Signal shapes for $ {m_{\gamma \gamma}} $ (left) and $ {m_\text {jj}}$ (right) in the SM HH nonresonant sample after full analysis selection in the high-mass and HPC region. The solid line shows a fit to the simulated data points with a double-sided CB function. The normalization of the shapes is arbitrary.

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Figure 6-a:
Signal shape for $ {m_{\gamma \gamma}} $ in the SM HH nonresonant sample after full analysis selection in the high-mass and HPC region. The solid line shows a fit to the simulated data points with a double-sided CB function. The normalization of the shapes is arbitrary.

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Figure 6-b:
Signal shape for $ {m_\text {jj}}$ in the SM HH nonresonant sample after full analysis selection in the high-mass and HPC region. The solid line shows a fit to the simulated data points with a double-sided CB function. The normalization of the shapes is arbitrary.

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Figure 7:
Background fits for the SM HH nonresonant analysis selection in the HM region. The plots on the left (right) show the distributions in the HPC (MPC) region. Top plots show the $ {m_{\gamma \gamma}} $ spectra and bottom ones the $ {m_\text {jj}}$.

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Figure 7-a:
Background fit for the SM HH nonresonant analysis selection in the HM region. The plot shows the $ {m_{\gamma \gamma}} $ spectrum in the HPC region.

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Figure 7-b:
Background fit for the SM HH nonresonant analysis selection in the HM region. The plot shows the $ {m_{\gamma \gamma}} $ spectrum in the MPC region.

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Figure 7-c:
Background fit for the SM HH nonresonant analysis selection in the HM region. The plot shows the $ {m_\text {jj}}$ spectrum in the HPC region.

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Figure 7-d:
Background fit for the SM HH nonresonant analysis selection in the HM region. The plot shows the $ {m_\text {jj}}$ spectrum in the MPC region.

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Figure 8:
Background fits for the SM HH nonresonant analysis selection in the LM region. The plots on the left (right) show the distributions in the HPC (MPC) region. Top plots show the $ {m_{\gamma \gamma}} $ spectra and bottom ones the $ {m_\text {jj}}$.

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Figure 8-a:
Background fit for the SM HH nonresonant analysis selection in the LM region. The plot shows the $ {m_{\gamma \gamma}} $ spectrum in the HPC region.

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Figure 8-b:
Background fit for the SM HH nonresonant analysis selection in the LM region. The plot shows the $ {m_{\gamma \gamma}} $ spectrum in the MPC region.

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Figure 8-c:
Background fit for the SM HH nonresonant analysis selection in the LM region. The plot shows the $ {m_\text {jj}}$ spectrum in the HPC region.

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Figure 8-d:
Background fit for the SM HH nonresonant analysis selection in the LM region. The plot shows the $ {m_\text {jj}}$ spectrum in the MPC region.

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Figure 9:
Observed and expected 95% CL upper limits on the product of cross section and branching fraction $\sigma ({\mathrm {p}} {\mathrm {p}}\to \text {X}) \mathcal {B}(\text {X} \to {{{\mathrm {H}} {\mathrm {H}}}} \to \gamma \gamma {{\mathrm {b}} {\overline {\mathrm {b}}}})$ obtained through a combination of the two analysis categories (HPC and MPC) for spin-0 (left) and spin-2 (right) hypotheses. The green and yellow bands represent, respectively, the one and two standard deviation extensions beyond the expected limit. Also shown are theoretical predictions corresponding to WED models for bulk radions (top) and bulk KK gravitons (bottom). The vertical dashed lines show the boundary between the low- and high-mass regions. The limits for $ {m_\text {X}} = $ 600 GeV are shown for both methods.

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Figure 9-a:
Observed and expected 95% CL upper limits on the product of cross section and branching fraction $\sigma ({\mathrm {p}} {\mathrm {p}}\to \text {X}) \mathcal {B}(\text {X} \to {{{\mathrm {H}} {\mathrm {H}}}} \to \gamma \gamma {{\mathrm {b}} {\overline {\mathrm {b}}}})$ obtained through a combination of the two analysis categories (HPC and MPC) for the spin-0 hypothesis. The green and yellow bands represent, respectively, the one and two standard deviation extensions beyond the expected limit. Also shown are theoretical predictions corresponding to WED models for bulk radions. The vertical dashed lines show the boundary between the low- and high-mass regions. The limits for $ {m_\text {X}} = $ 600 GeV are shown for both methods.

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Figure 9-b:
Observed and expected 95% CL upper limits on the product of cross section and branching fraction $\sigma ({\mathrm {p}} {\mathrm {p}}\to \text {X}) \mathcal {B}(\text {X} \to {{{\mathrm {H}} {\mathrm {H}}}} \to \gamma \gamma {{\mathrm {b}} {\overline {\mathrm {b}}}})$ obtained through a combination of the two analysis categories (HPC and MPC) for the spin-2 hypothesis. The green and yellow bands represent, respectively, the one and two standard deviation extensions beyond the expected limit. Also shown are theoretical predictions corresponding to WED models for KK gravitons. The vertical dashed lines show the boundary between the low- and high-mass regions. The limits for $ {m_\text {X}} = $ 600 GeV are shown for both methods.

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Figure 10:
Expected and observed 95% CL upper limits on the SM-like HH production cross section times $\mathcal {B}({{{\mathrm {H}} {\mathrm {H}}}} \to {\gamma \gamma {{\mathrm {b}} {\overline {\mathrm {b}}}}})$ obtained for different nonresonant benchmark models (defined in Table 1) (top); for different values of the $ {\kappa _{\lambda}} $ (bottom). The red line in the bottom plot shows the prediction of theory with the associated uncertainties shown as the orange band.

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Figure 10-a:
Expected and observed 95% CL upper limits on the SM-like HH production cross section times $\mathcal {B}({{{\mathrm {H}} {\mathrm {H}}}} \to {\gamma \gamma {{\mathrm {b}} {\overline {\mathrm {b}}}}})$ obtained for different nonresonant benchmark models (defined in Table 1).

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Figure 10-b:
Expected and observed 95% CL upper limits on the SM-like HH production cross section times $\mathcal {B}({{{\mathrm {H}} {\mathrm {H}}}} \to {\gamma \gamma {{\mathrm {b}} {\overline {\mathrm {b}}}}})$ obtained for different values of the $ {\kappa _{\lambda}} $ (bottom). The red line shows the prediction of theory with the associated uncertainties shown as the orange band.
Tables

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Table 1:
Parameter values of nonresonant BSM benchmark hypotheses. The first two columns correspond to the SM and $ {\kappa _{\lambda}} = $ 0 samples, while the next 12 correspond to the benchmark hypotheses identified using the method from Ref. [43].

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Table 2:
Summary of the baseline selection criteria.

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Table 3:
Definition of high-purity category (HPC) and medium-purity category (MPC) for the resonant and nonresonant analyses.

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Table 4:
Summary of systematic uncertainties.
Summary
A search is performed by the CMS Collaboration for the resonant and nonresonant production of a pair of Higgs bosons in the decay channel ${{\mathrm{H}\mathrm{H}}} \to {\gamma\gamma\mathrm{b\bar{b}}} $, based on an integrated luminosity of 35.9 fb$^{-1}$ of pp collisions collected at $\sqrt{s} = $ 13 TeV in 2016. No statistically significant deviations from the standard model (SM) predictions are found. Upper limits at a 95% CL are set on the cross sections for the production of new particles decaying to two Higgs bosons in the mass range between 250 and 900 GeV, under the spin-0 and spin-2 hypotheses. In the case of beyond SM predictions, based on the assumption of the existence of a warped extra dimension, we exclude the radion (spin-0) signal hypothesis, assuming the scale parameter ${\Lambda}_{\mathrm{R}} = $ 3 TeV, for all masses below ${m_\text{X}} = $ 540 GeV, and the KK graviton (spin-2) hypothesis for the mass range 290 $ < {m_\text{X}} < $ 810 GeV, assuming ${\kappa/\overline{{{M_\mathrm{Pl}}}}} = $ 1.0 ($\overline{{{M_\mathrm{Pl}}}}$ being the reduced Planck mass and $\kappa$ the warp factor of the metric). For nonresonant production with SM-like kinematics, a 95% CL upper limit of 2.0 fb is set on $\sigma({\mathrm{p}}{\mathrm{p}\to{{\mathrm{H}\mathrm{H}}} \to{\gamma\gamma\mathrm{b\bar{b}}}} )$, corresponding to about 24 times the SM prediction. Anomalous couplings of the Higgs boson are also investigated, as well as the vector boson fusion ${{\mathrm{H}\mathrm{H}}} $ production process. Values of the effective Higgs boson self-coupling ${\kappa_{\lambda}} $ are constrained to be within the range $-11 < {\kappa_{\lambda}} < 17$ at 95% CL, assuming all other Higgs boson couplings to be at their SM values. The direct constraints reported on SM-like production and ${\kappa_{\lambda}} $ are the most restrictive to date.
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