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| CMS-HIG-22-013 ; CERN-EP-2025-124 | ||
| Search for heavy pseudoscalar and scalar bosons decaying to a top quark pair in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 8 July 2025 | ||
| Accepted for publication in Reports on Progress in Physics | ||
| Abstract: A search for pseudoscalar or scalar bosons decaying to a top quark pair ($ \mathrm{t} \overline{\mathrm{t}} $) in final states with one or two charged leptons is presented. The analyzed proton-proton collision data was recorded at $ \sqrt{s}= $ 13 TeV by the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 138 fb$ ^{-1} $. The invariant mass $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ of the reconstructed $ \mathrm{t} \overline{\mathrm{t}} $ system and variables sensitive to its spin and parity are used to discriminate against the standard model $ \mathrm{t} \overline{\mathrm{t}} $ background. Interference between pseudoscalar or scalar boson production and the standard model $ \mathrm{t} \overline{\mathrm{t}} $ continuum is included, leading to peak-dip structures in the $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distribution. An excess of the data above the background prediction, based on perturbative quantum chromodynamics (QCD) calculations, is observed near the kinematic $ \mathrm{t} \overline{\mathrm{t}} $ production threshold, while good agreement is found for high $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $. The data are consistent with the background prediction if the contribution from the production of a color-singlet $ ^1\mathrm{S}_0^{[1]} $\ $ \mathrm{t} \overline{\mathrm{t}} $ quasi-bound state $ \eta_{\mathrm{t}}$, predicted by nonrelativistic QCD, is added. Upper limits at 95% confidence level are set on the coupling between the pseudoscalar or scalar bosons and the top quark for boson masses in the range 365-1000 GeV, relative widths between 0.5 and 25%, and two background scenarios with or without $ \eta_{\mathrm{t}}$ contribution. | ||
| Links: e-print arXiv:2507.05119 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Example Feynman diagrams for the signal process (left) and for SM $ \mathrm{t} \overline{\mathrm{t}} $ production (right). |
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Figure 1-a:
Example Feynman diagrams for the signal process (left) and for SM $ \mathrm{t} \overline{\mathrm{t}} $ production (right). |
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Figure 1-b:
Example Feynman diagrams for the signal process (left) and for SM $ \mathrm{t} \overline{\mathrm{t}} $ production (right). |
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Figure 2:
Differential cross section of $ \mathrm{t} \overline{\mathrm{t}} $ production at parton level as a function of $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $, shown as difference between various BSM scenarios and the SM prediction. Shown are the cases of a single A (red) or H (blue) boson for two example configurations: $ m_{\Phi}= $ 400 GeV and $ \Gamma_{\Phi}/m_{\Phi}=5% $ (left), or $ m_{\Phi}= $ 800 GeV and $ \Gamma_{\Phi}/m_{\Phi}=10% $ (right), with $ g_{\Phi\mathrm{tt}} = $ 1 in both cases. Separately shown are the cases where only the resonant $ \Phi\to{\mathrm{t}\overline{\mathrm{t}}} $ contribution is added to the SM prediction (dashed), where only the interference between SM and $ \Phi $ boson contributions is added (dotted), and where both contributions are added (solid). The distributions have been calculated using MadGraph-5_aMC@NLO as described in Section 3. |
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Figure 2-a:
Differential cross section of $ \mathrm{t} \overline{\mathrm{t}} $ production at parton level as a function of $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $, shown as difference between various BSM scenarios and the SM prediction. Shown are the cases of a single A (red) or H (blue) boson for two example configurations: $ m_{\Phi}= $ 400 GeV and $ \Gamma_{\Phi}/m_{\Phi}=5% $ (left), or $ m_{\Phi}= $ 800 GeV and $ \Gamma_{\Phi}/m_{\Phi}=10% $ (right), with $ g_{\Phi\mathrm{tt}} = $ 1 in both cases. Separately shown are the cases where only the resonant $ \Phi\to{\mathrm{t}\overline{\mathrm{t}}} $ contribution is added to the SM prediction (dashed), where only the interference between SM and $ \Phi $ boson contributions is added (dotted), and where both contributions are added (solid). The distributions have been calculated using MadGraph-5_aMC@NLO as described in Section 3. |
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Figure 2-b:
Differential cross section of $ \mathrm{t} \overline{\mathrm{t}} $ production at parton level as a function of $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $, shown as difference between various BSM scenarios and the SM prediction. Shown are the cases of a single A (red) or H (blue) boson for two example configurations: $ m_{\Phi}= $ 400 GeV and $ \Gamma_{\Phi}/m_{\Phi}=5% $ (left), or $ m_{\Phi}= $ 800 GeV and $ \Gamma_{\Phi}/m_{\Phi}=10% $ (right), with $ g_{\Phi\mathrm{tt}} = $ 1 in both cases. Separately shown are the cases where only the resonant $ \Phi\to{\mathrm{t}\overline{\mathrm{t}}} $ contribution is added to the SM prediction (dashed), where only the interference between SM and $ \Phi $ boson contributions is added (dotted), and where both contributions are added (solid). The distributions have been calculated using MadGraph-5_aMC@NLO as described in Section 3. |
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Figure 3:
Comparison of the number of observed (points) and expected (colored histograms) events in the $ \ell{\mathrm{j}} $ channel after the kinematic reconstruction and background estimation for the distributions of the reconstructed hadronic top quark mass $ m_{\mathrm{t}}^{\text{had}} $ in the region with four or more jets (left) and the $ p_{\mathrm{T}} $ of the $ \mathrm{t} \overline{\mathrm{t}} $ system in the region with exactly three jets (right). The ratio to the total prediction is shown in the lower panel, and the total systematic uncertainty is shown as the gray band. |
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Figure 3-a:
Comparison of the number of observed (points) and expected (colored histograms) events in the $ \ell{\mathrm{j}} $ channel after the kinematic reconstruction and background estimation for the distributions of the reconstructed hadronic top quark mass $ m_{\mathrm{t}}^{\text{had}} $ in the region with four or more jets (left) and the $ p_{\mathrm{T}} $ of the $ \mathrm{t} \overline{\mathrm{t}} $ system in the region with exactly three jets (right). The ratio to the total prediction is shown in the lower panel, and the total systematic uncertainty is shown as the gray band. |
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Figure 3-b:
Comparison of the number of observed (points) and expected (colored histograms) events in the $ \ell{\mathrm{j}} $ channel after the kinematic reconstruction and background estimation for the distributions of the reconstructed hadronic top quark mass $ m_{\mathrm{t}}^{\text{had}} $ in the region with four or more jets (left) and the $ p_{\mathrm{T}} $ of the $ \mathrm{t} \overline{\mathrm{t}} $ system in the region with exactly three jets (right). The ratio to the total prediction is shown in the lower panel, and the total systematic uncertainty is shown as the gray band. |
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Figure 4:
Normalized differential cross sections in the spin correlation observables $ c_{\text{hel}} $ (left) and $ c_{\text{han}} $ (right) at the parton level in the $ \ell\ell $ channel, with no requirements on acceptance, for SM $ \mathrm{t} \overline{\mathrm{t}} $ production (black solid), resonant A boson production (red dashed), and resonant H boson production (blue dotted). The corresponding distributions for $ \eta_{\mathrm{t}}$ are identical to those of a A boson. |
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Figure 4-a:
Normalized differential cross sections in the spin correlation observables $ c_{\text{hel}} $ (left) and $ c_{\text{han}} $ (right) at the parton level in the $ \ell\ell $ channel, with no requirements on acceptance, for SM $ \mathrm{t} \overline{\mathrm{t}} $ production (black solid), resonant A boson production (red dashed), and resonant H boson production (blue dotted). The corresponding distributions for $ \eta_{\mathrm{t}}$ are identical to those of a A boson. |
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Figure 4-b:
Normalized differential cross sections in the spin correlation observables $ c_{\text{hel}} $ (left) and $ c_{\text{han}} $ (right) at the parton level in the $ \ell\ell $ channel, with no requirements on acceptance, for SM $ \mathrm{t} \overline{\mathrm{t}} $ production (black solid), resonant A boson production (red dashed), and resonant H boson production (blue dotted). The corresponding distributions for $ \eta_{\mathrm{t}}$ are identical to those of a A boson. |
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Figure 5:
Comparison of the number of observed (points) and expected (colored histograms) events in the $ \ell\ell $ channel after the kinematic reconstruction and background estimation for the distributions of the invariant lepton-b jet mass $ m_{\ell\mathrm{b}} $ (left) and the $ p_{\mathrm{T}} $ of the $ \mathrm{t} \overline{\mathrm{t}} $ system (right). The ratio to the total prediction is shown in the lower panel, and the total systematic uncertainty is shown as the gray band. |
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Figure 5-a:
Comparison of the number of observed (points) and expected (colored histograms) events in the $ \ell\ell $ channel after the kinematic reconstruction and background estimation for the distributions of the invariant lepton-b jet mass $ m_{\ell\mathrm{b}} $ (left) and the $ p_{\mathrm{T}} $ of the $ \mathrm{t} \overline{\mathrm{t}} $ system (right). The ratio to the total prediction is shown in the lower panel, and the total systematic uncertainty is shown as the gray band. |
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Figure 5-b:
Comparison of the number of observed (points) and expected (colored histograms) events in the $ \ell\ell $ channel after the kinematic reconstruction and background estimation for the distributions of the invariant lepton-b jet mass $ m_{\ell\mathrm{b}} $ (left) and the $ p_{\mathrm{T}} $ of the $ \mathrm{t} \overline{\mathrm{t}} $ system (right). The ratio to the total prediction is shown in the lower panel, and the total systematic uncertainty is shown as the gray band. |
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Figure 6:
Observed and expected $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distribution in bins of $ \lvert\cos\theta^\ast_{\mathrm{t}_{\ell}}\rvert $, shown for the $ \ell+3{\mathrm{j}} $ channel summed over lepton flavors and eras. In the upper panel, the data (points with statistical error bars) are compared to $ \mathrm{t} \overline{\mathrm{t}} $ production in FO pQCD and other sources of background (colored histograms) after the fit to the data in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ interpretation. The ratio of data to the prediction is shown in the middle panel, where the two signals $\mathrm{A}(365,\,2\%)$ and $\mathrm{H}(425,\,3\%)$, corresponding to the best fit point, are overlaid. The lower panel shows the equivalent ratio for the fit where $ \eta_{\mathrm{t}}$ is considered as an additional background, for the same signal points. In both cases, the gray band shows the postfit uncertainty, and the respective signals are overlaid with their best fit model parameters. |
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Figure 7:
Observed and expected $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distribution in $ \lvert\cos\theta^\ast_{\mathrm{t}_{\ell}}\rvert $ bins, shown for the $ \ell+{\geq}4{\mathrm{j}} $ channel summed over lepton flavors and eras. Notations as in Fig. 6. |
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Figure 8:
Observed and expected $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distribution in $ c_{\text{hel}} $ and $ c_{\text{han}} $ bins, shown for the $ \ell\ell $ channel summed over lepton flavors and eras. Notations as in Fig. 6. |
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Figure 9:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ for the $\mathrm{A}(365,\,2\%)$+$\mathrm{H}(425,\,3\%)$ signal point, in the background scenario excluding (left) and including (right) $ \eta_{\mathrm{t}}$ production. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in black and pink, respectively, with different line styles denoting progressively higher $ \text{CL}_\text{s} $. The regions outside of the contours are considered excluded. |
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Figure 9-a:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ for the $\mathrm{A}(365,\,2\%)$+$\mathrm{H}(425,\,3\%)$ signal point, in the background scenario excluding (left) and including (right) $ \eta_{\mathrm{t}}$ production. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in black and pink, respectively, with different line styles denoting progressively higher $ \text{CL}_\text{s} $. The regions outside of the contours are considered excluded. |
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Figure 9-b:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ for the $\mathrm{A}(365,\,2\%)$+$\mathrm{H}(425,\,3\%)$ signal point, in the background scenario excluding (left) and including (right) $ \eta_{\mathrm{t}}$ production. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in black and pink, respectively, with different line styles denoting progressively higher $ \text{CL}_\text{s} $. The regions outside of the contours are considered excluded. |
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Figure 10:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, for $ \Gamma_{\Phi}/m_{\Phi} $ of 1, 2, 5, 10, 18, and 25% (from upper left to lower right). The observed constraints are indicated by the shaded blue area, bounded by the solid blue curve. The inner green and outer yellow bands indicate the regions containing 68 and 95%, respectively, of the distribution of constraints expected under the background-only hypothesis. The unphysical region of phase space in which the partial width $ \Gamma_{\mathrm{A}\to{\mathrm{t}\overline{\mathrm{t}}} } $ becomes larger than the total width of the A boson is indicated by the hatched line. |
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Figure 10-a:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, for $ \Gamma_{\Phi}/m_{\Phi} $ of 1, 2, 5, 10, 18, and 25% (from upper left to lower right). The observed constraints are indicated by the shaded blue area, bounded by the solid blue curve. The inner green and outer yellow bands indicate the regions containing 68 and 95%, respectively, of the distribution of constraints expected under the background-only hypothesis. The unphysical region of phase space in which the partial width $ \Gamma_{\mathrm{A}\to{\mathrm{t}\overline{\mathrm{t}}} } $ becomes larger than the total width of the A boson is indicated by the hatched line. |
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Figure 10-b:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, for $ \Gamma_{\Phi}/m_{\Phi} $ of 1, 2, 5, 10, 18, and 25% (from upper left to lower right). The observed constraints are indicated by the shaded blue area, bounded by the solid blue curve. The inner green and outer yellow bands indicate the regions containing 68 and 95%, respectively, of the distribution of constraints expected under the background-only hypothesis. The unphysical region of phase space in which the partial width $ \Gamma_{\mathrm{A}\to{\mathrm{t}\overline{\mathrm{t}}} } $ becomes larger than the total width of the A boson is indicated by the hatched line. |
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Figure 10-c:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, for $ \Gamma_{\Phi}/m_{\Phi} $ of 1, 2, 5, 10, 18, and 25% (from upper left to lower right). The observed constraints are indicated by the shaded blue area, bounded by the solid blue curve. The inner green and outer yellow bands indicate the regions containing 68 and 95%, respectively, of the distribution of constraints expected under the background-only hypothesis. The unphysical region of phase space in which the partial width $ \Gamma_{\mathrm{A}\to{\mathrm{t}\overline{\mathrm{t}}} } $ becomes larger than the total width of the A boson is indicated by the hatched line. |
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Figure 10-d:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, for $ \Gamma_{\Phi}/m_{\Phi} $ of 1, 2, 5, 10, 18, and 25% (from upper left to lower right). The observed constraints are indicated by the shaded blue area, bounded by the solid blue curve. The inner green and outer yellow bands indicate the regions containing 68 and 95%, respectively, of the distribution of constraints expected under the background-only hypothesis. The unphysical region of phase space in which the partial width $ \Gamma_{\mathrm{A}\to{\mathrm{t}\overline{\mathrm{t}}} } $ becomes larger than the total width of the A boson is indicated by the hatched line. |
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Figure 10-e:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, for $ \Gamma_{\Phi}/m_{\Phi} $ of 1, 2, 5, 10, 18, and 25% (from upper left to lower right). The observed constraints are indicated by the shaded blue area, bounded by the solid blue curve. The inner green and outer yellow bands indicate the regions containing 68 and 95%, respectively, of the distribution of constraints expected under the background-only hypothesis. The unphysical region of phase space in which the partial width $ \Gamma_{\mathrm{A}\to{\mathrm{t}\overline{\mathrm{t}}} } $ becomes larger than the total width of the A boson is indicated by the hatched line. |
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Figure 10-f:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, for $ \Gamma_{\Phi}/m_{\Phi} $ of 1, 2, 5, 10, 18, and 25% (from upper left to lower right). The observed constraints are indicated by the shaded blue area, bounded by the solid blue curve. The inner green and outer yellow bands indicate the regions containing 68 and 95%, respectively, of the distribution of constraints expected under the background-only hypothesis. The unphysical region of phase space in which the partial width $ \Gamma_{\mathrm{A}\to{\mathrm{t}\overline{\mathrm{t}}} } $ becomes larger than the total width of the A boson is indicated by the hatched line. |
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Figure 11:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 11-a:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 11-b:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 11-c:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 11-d:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 11-e:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 11-f:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario without $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 12:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 12-a:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 12-b:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 12-c:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 12-d:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 12-e:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 12-f:
Model-independent constraints on $g_{\mathrm{At\bar{t}}}$ as functions of the A boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 13:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 13-a:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 13-b:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 13-c:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 13-d:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 13-e:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 13-f:
Model-independent constraints on $g_{\mathrm{Ht\bar{t}}}$ as functions of the H boson mass in the background scenario with $ \eta_{\mathrm{t}}$ contribution, shown in the same fashion as in Fig. 10. |
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Figure 14:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for four different signal hypotheses with identical A and H boson masses of 365 GeV (upper left), 500 GeV (upper right), 750 GeV (lower left), and 1000 GeV (lower right), all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
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Figure 14-a:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for four different signal hypotheses with identical A and H boson masses of 365 GeV (upper left), 500 GeV (upper right), 750 GeV (lower left), and 1000 GeV (lower right), all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
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Figure 14-b:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for four different signal hypotheses with identical A and H boson masses of 365 GeV (upper left), 500 GeV (upper right), 750 GeV (lower left), and 1000 GeV (lower right), all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
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Figure 14-c:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for four different signal hypotheses with identical A and H boson masses of 365 GeV (upper left), 500 GeV (upper right), 750 GeV (lower left), and 1000 GeV (lower right), all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
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Figure 14-d:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for four different signal hypotheses with identical A and H boson masses of 365 GeV (upper left), 500 GeV (upper right), 750 GeV (lower left), and 1000 GeV (lower right), all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
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Figure 15:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for six different signal hypotheses with unequal A and H boson masses, corresponding to combinations of 365, 500, and 1000 GeV, all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
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Figure 15-a:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for six different signal hypotheses with unequal A and H boson masses, corresponding to combinations of 365, 500, and 1000 GeV, all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
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Figure 15-b:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for six different signal hypotheses with unequal A and H boson masses, corresponding to combinations of 365, 500, and 1000 GeV, all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
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Figure 15-c:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for six different signal hypotheses with unequal A and H boson masses, corresponding to combinations of 365, 500, and 1000 GeV, all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
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Figure 15-d:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for six different signal hypotheses with unequal A and H boson masses, corresponding to combinations of 365, 500, and 1000 GeV, all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
png pdf |
Figure 15-e:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for six different signal hypotheses with unequal A and H boson masses, corresponding to combinations of 365, 500, and 1000 GeV, all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
png pdf |
Figure 15-f:
Frequentist 2D exclusion contours for $g_{\mathrm{At\bar{t}}}$ and $g_{\mathrm{Ht\bar{t}}}$ in the $ {\mathrm{A}}\text{+}{\mathrm{H}} $ boson interpretation for six different signal hypotheses with unequal A and H boson masses, corresponding to combinations of 365, 500, and 1000 GeV, all assuming a relative width of 2%. The expected and observed contours, evaluated with the Feldman-Cousins prescription [126,127], are shown in pink and black, respectively, with the solid and dashed lines corresponding to exclusions at 68 and 95% CL. The regions outside of the contours are considered excluded. In all cases, $ \eta_{\mathrm{t}}$ production is included in the background model. |
| Tables | |
png pdf |
Table 1:
The systematic uncertainties considered in the analysis, indicating in parenthesis the number of corresponding nuisance parameters in the statistical model (if more than one), the type (affecting only normalization or also the shape of the search templates), and the affected physics processes and analysis channels they are applicable to. |
| Summary |
| A search has been presented for the production of pseudoscalar or scalar bosons in proton-proton collisions at $ \sqrt{s}= $ 13 TeV, decaying into a top quark pair ($ \mathrm{t} \overline{\mathrm{t}} $) in final states with one or two charged leptons. The analysis uses data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. To discriminate the signal from the standard model $ \mathrm{t} \overline{\mathrm{t}} $ background, the search utilizes the invariant mass of the reconstructed $ \mathrm{t} \overline{\mathrm{t}} $ system along with angular observables sensitive to its spin and parity. The signal model accounts for both the resonant production of the new boson and its interference with the perturbative quantum chromodynamics (pQCD) $ \mathrm{t} \overline{\mathrm{t}} $ background. A deviation from the background prediction, modeled using fixed-order (FO) pQCD, is observed near the $ \mathrm{t} \overline{\mathrm{t}} $ production threshold. This deviation is similar to the moderate excess previously reported by CMS using data corresponding to an integrated luminosity of 35.9 fb$ ^{-1} $ [28]. The local significance of the excess exceeds five standard deviations, with a strong preference for the pseudoscalar signal hypothesis over the scalar one. Incorporating the production of a color-singlet $ ^1\mathrm{S}_0^{[1]} $\ $ \mathrm{t} \overline{\mathrm{t}} $ quasi-bound state, $ \eta_{\mathrm{t}}$, within a simplified nonrelativistic QCD model, with an unconstrained normalization to the background, yields agreement with the observed data, eliminating the need for additional exotic pseudoscalar or scalar boson production. However, the precision of the measurement is insufficient to clearly favor either the $ \eta_{\mathrm{t}}$ production model, or a new A boson down to a mass of 365 GeV, or any potential mixture of the two. A detailed analysis of the excess using the $ \mathrm{t} \overline{\mathrm{t}} $ quasi-bound-state interpretation is provided in Ref. [27]. Exclusion limits at the 95% confidence level are set on the coupling strength between top quarks and new bosons, covering mass ranges of 365-1000 GeV and relative widths of 0.5-25%. When the background model includes both FO pQCD $ \mathrm{t} \overline{\mathrm{t}} $ production and $ \eta_{\mathrm{t}}$ production, stringent constraints are obtained for three scenarios: a new pseudoscalar boson, a new scalar boson, and the simultaneous presence of both. Coupling values as low as 0.4 (0.6) are excluded for the pseudoscalar (scalar) case. These limits are similar to the ATLAS results [30] in case of pseudoscalar production, and represent the most stringent limits on scalar resonances decaying into $ \mathrm{t} \overline{\mathrm{t}} $ over a wide range of mass and width values. |
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