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| CMS-B2G-25-009 ; CERN-EP-2026-049 | ||
| Search for new particles decaying into top quark-antiquark pairs in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 24 March 2026 | ||
| Submitted to the Journal of High Energy Physics | ||
| Abstract: A search for new particles decaying to top quark-antiquark pairs is performed using proton-proton collision data at a centre-of-mass energy of 13 TeV. The data set recorded with the CMS detector between 2016 and 2018 is used, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. Final states with 0, 1, and 2 leptons are analyzed, covering all decay modes of the top quark-antiquark pairs. Heavy $ \mathrm{Z}^{'} $ bosons with relative widths of 1, 10, and 30% are excluded for masses in the ranges 0.4--4.8, 0.4--6.2, and 0.4--7.4 TeV, respectively. A Kaluza--Klein gluon in the Randall--Sundrum model and a dark-matter mediator are excluded for masses between 0.5--5.5 and 1.0--4.2 TeV, respectively. These results set the most stringent limits to date for the considered models in the $ \mathrm{t} \overline{\mathrm{t}} $ final state. In addition, in the two-Higgs-doublet models, upper limits are set on the coupling strength modifier for scalar and pseudoscalar Higgs bosons with relative widths of 2.5, 10, and 25% in the mass range of 0.5--1.0 TeV. | ||
| Links: e-print arXiv:2603.23454 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Example Feynman diagrams at leading order for the production and decay of a spin-1 $ \mathrm{Z}^{'} /g_{KK}$ boson (left) and a scalar H or pseudoscalar $ \mathrm{A} $ resonance (right). |
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Figure 1-a:
Example Feynman diagrams at leading order for the production and decay of a spin-1 $ \mathrm{Z}^{'} /g_{KK}$ boson (left) and a scalar H or pseudoscalar $ \mathrm{A} $ resonance (right). |
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Figure 1-b:
Example Feynman diagrams at leading order for the production and decay of a spin-1 $ \mathrm{Z}^{'} /g_{KK}$ boson (left) and a scalar H or pseudoscalar $ \mathrm{A} $ resonance (right). |
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Figure 2:
Illustration of the background estimation method. The data set is binned in the leading jet mass $ m_{\mathrm{t}} $ and in the reconstructed $ \mathrm{t} \overline{\mathrm{t}} $ invariant mass $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $. Disjoint regions are defined according to whether $ m_{\mathrm{t}} $ lies inside or outside the top quark mass window and whether the subleading jet passes or fails the $ \mathrm{t}\text{ tagging} $ requirement. A method based on control samples in data is used to estimate the QCD background in the signal region E from regions A, B, C, D, and F. The colored dotted points are shown for illustrative purposes only. |
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Figure 3:
Prefit data-to-simulation comparison of distributions in the all-hadronic channel for the mass of the leading $ \mathrm{t}\text{ tagged} $ jet (left) and the reconstructed $ \mathrm{t} \overline{\mathrm{t}} $ mass (right) in the central and forward categories combined, where both jets pass the $ \mathrm{t}\text{ tagging} $ requirement. The QCD background is taken from simulation for comparison, whereas in the analysis it is estimated from data. No cut on the $ m_{\mathrm{t}} $ variable is applied. |
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Figure 3-a:
Prefit data-to-simulation comparison of distributions in the all-hadronic channel for the mass of the leading $ \mathrm{t}\text{ tagged} $ jet (left) and the reconstructed $ \mathrm{t} \overline{\mathrm{t}} $ mass (right) in the central and forward categories combined, where both jets pass the $ \mathrm{t}\text{ tagging} $ requirement. The QCD background is taken from simulation for comparison, whereas in the analysis it is estimated from data. No cut on the $ m_{\mathrm{t}} $ variable is applied. |
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Figure 3-b:
Prefit data-to-simulation comparison of distributions in the all-hadronic channel for the mass of the leading $ \mathrm{t}\text{ tagged} $ jet (left) and the reconstructed $ \mathrm{t} \overline{\mathrm{t}} $ mass (right) in the central and forward categories combined, where both jets pass the $ \mathrm{t}\text{ tagging} $ requirement. The QCD background is taken from simulation for comparison, whereas in the analysis it is estimated from data. No cut on the $ m_{\mathrm{t}} $ variable is applied. |
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Figure 4:
Reconstructed $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distributions in simulation in the all-hadronic channel for $ \mathrm{Z}^{'} $ bosons with 1 and 30% relative widths, shown in the left and right panels, respectively. The signals correspond to $ \mathrm{Z}^{'} $ boson masses of 2, 4, and 6 TeV, where both jets pass the $ \mathrm{t}\text{ tagging} $ requirement. Signals are normalized to a cross section of 1\unitpb and an integrated luminosity of 138 fb$ ^{-1} $. No cut on the $ m_{\mathrm{t}} $ variable is applied. |
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Figure 4-a:
Reconstructed $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distributions in simulation in the all-hadronic channel for $ \mathrm{Z}^{'} $ bosons with 1 and 30% relative widths, shown in the left and right panels, respectively. The signals correspond to $ \mathrm{Z}^{'} $ boson masses of 2, 4, and 6 TeV, where both jets pass the $ \mathrm{t}\text{ tagging} $ requirement. Signals are normalized to a cross section of 1\unitpb and an integrated luminosity of 138 fb$ ^{-1} $. No cut on the $ m_{\mathrm{t}} $ variable is applied. |
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Figure 4-b:
Reconstructed $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distributions in simulation in the all-hadronic channel for $ \mathrm{Z}^{'} $ bosons with 1 and 30% relative widths, shown in the left and right panels, respectively. The signals correspond to $ \mathrm{Z}^{'} $ boson masses of 2, 4, and 6 TeV, where both jets pass the $ \mathrm{t}\text{ tagging} $ requirement. Signals are normalized to a cross section of 1\unitpb and an integrated luminosity of 138 fb$ ^{-1} $. No cut on the $ m_{\mathrm{t}} $ variable is applied. |
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Figure 5:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ for data and simulation for the central (left) and forward (right) categories for the all-hadronic channel, under the background-only hypothesis. Distributions are shown for the low-$ m_{\mathrm{t}} $ (upper) and high-$ m_{\mathrm{t}} $ (middle) sidebands, as well as the SR (lower). The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds in the signal regions. The lower panels show the pulls, defined as (Data - Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 5-a:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ for data and simulation for the central (left) and forward (right) categories for the all-hadronic channel, under the background-only hypothesis. Distributions are shown for the low-$ m_{\mathrm{t}} $ (upper) and high-$ m_{\mathrm{t}} $ (middle) sidebands, as well as the SR (lower). The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds in the signal regions. The lower panels show the pulls, defined as (Data - Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 5-b:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ for data and simulation for the central (left) and forward (right) categories for the all-hadronic channel, under the background-only hypothesis. Distributions are shown for the low-$ m_{\mathrm{t}} $ (upper) and high-$ m_{\mathrm{t}} $ (middle) sidebands, as well as the SR (lower). The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds in the signal regions. The lower panels show the pulls, defined as (Data - Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 5-c:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ for data and simulation for the central (left) and forward (right) categories for the all-hadronic channel, under the background-only hypothesis. Distributions are shown for the low-$ m_{\mathrm{t}} $ (upper) and high-$ m_{\mathrm{t}} $ (middle) sidebands, as well as the SR (lower). The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds in the signal regions. The lower panels show the pulls, defined as (Data - Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 5-d:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ for data and simulation for the central (left) and forward (right) categories for the all-hadronic channel, under the background-only hypothesis. Distributions are shown for the low-$ m_{\mathrm{t}} $ (upper) and high-$ m_{\mathrm{t}} $ (middle) sidebands, as well as the SR (lower). The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds in the signal regions. The lower panels show the pulls, defined as (Data - Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 5-e:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ for data and simulation for the central (left) and forward (right) categories for the all-hadronic channel, under the background-only hypothesis. Distributions are shown for the low-$ m_{\mathrm{t}} $ (upper) and high-$ m_{\mathrm{t}} $ (middle) sidebands, as well as the SR (lower). The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds in the signal regions. The lower panels show the pulls, defined as (Data - Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 5-f:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ for data and simulation for the central (left) and forward (right) categories for the all-hadronic channel, under the background-only hypothesis. Distributions are shown for the low-$ m_{\mathrm{t}} $ (upper) and high-$ m_{\mathrm{t}} $ (middle) sidebands, as well as the SR (lower). The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds in the signal regions. The lower panels show the pulls, defined as (Data - Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 6:
Reconstructed invariant mass distribution in simulation in the single-lepton channel for $ \mathrm{Z}^{'} $ bosons with 1% relative width, for different mass hypotheses. Each distribution corresponds to a production cross section of 1 pb. |
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Figure 7:
Different contributions to the $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distribution in simulation in the single-lepton channel for scalar Higgs bosons with masses of 0.5 (left) and 1 TeV (right), and corresponding relative widths of 2.5 and 10%, respectively. Each distribution is normalized to the corresponding production cross section. |
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Figure 7-a:
Different contributions to the $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distribution in simulation in the single-lepton channel for scalar Higgs bosons with masses of 0.5 (left) and 1 TeV (right), and corresponding relative widths of 2.5 and 10%, respectively. Each distribution is normalized to the corresponding production cross section. |
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Figure 7-b:
Different contributions to the $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ distribution in simulation in the single-lepton channel for scalar Higgs bosons with masses of 0.5 (left) and 1 TeV (right), and corresponding relative widths of 2.5 and 10%, respectively. Each distribution is normalized to the corresponding production cross section. |
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Figure 8:
The DNN score distributions for the combined muon and electron channels in the single-lepton channel: $ \mathrm{t} \overline{\mathrm{t}} $ score (upper left), single t score (upper right), and V+jets score (lower). The lower panels show the ratio of the data to the total SM background prediction. The gray bands represent the uncertainty, computed by summing in quadrature the statistical uncertainty and the systematic uncertainties affecting the normalization of each process. These observables are not fitted to extract the final results; the uncertainties are the prefit values. |
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Figure 8-a:
The DNN score distributions for the combined muon and electron channels in the single-lepton channel: $ \mathrm{t} \overline{\mathrm{t}} $ score (upper left), single t score (upper right), and V+jets score (lower). The lower panels show the ratio of the data to the total SM background prediction. The gray bands represent the uncertainty, computed by summing in quadrature the statistical uncertainty and the systematic uncertainties affecting the normalization of each process. These observables are not fitted to extract the final results; the uncertainties are the prefit values. |
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Figure 8-b:
The DNN score distributions for the combined muon and electron channels in the single-lepton channel: $ \mathrm{t} \overline{\mathrm{t}} $ score (upper left), single t score (upper right), and V+jets score (lower). The lower panels show the ratio of the data to the total SM background prediction. The gray bands represent the uncertainty, computed by summing in quadrature the statistical uncertainty and the systematic uncertainties affecting the normalization of each process. These observables are not fitted to extract the final results; the uncertainties are the prefit values. |
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Figure 8-c:
The DNN score distributions for the combined muon and electron channels in the single-lepton channel: $ \mathrm{t} \overline{\mathrm{t}} $ score (upper left), single t score (upper right), and V+jets score (lower). The lower panels show the ratio of the data to the total SM background prediction. The gray bands represent the uncertainty, computed by summing in quadrature the statistical uncertainty and the systematic uncertainties affecting the normalization of each process. These observables are not fitted to extract the final results; the uncertainties are the prefit values. |
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Figure 9:
Distribution of $ \cos(\theta^\ast) $ for different processes in simulation in the single-lepton channel: SM $ \mathrm{t} \overline{\mathrm{t}} $ (solid red), $ \mathrm{Z}^{'} $ with $ m_{{\mathrm{t}\overline{\mathrm{t}}} }= $ 1.4 TeV (long-dashed orange), scalar H with $ m_{\mathrm{H}}= $ 1 TeV and 2.5% relative width (short-dashed green), and scalar H with $ m_{\mathrm{H}}= $ 1 TeV and 10% relative width (dash-dotted blue). All distributions are normalized to unit area. |
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Figure 10:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the single t (left) and V+jets (right) CRs, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 10-a:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the single t (left) and V+jets (right) CRs, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 10-b:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the single t (left) and V+jets (right) CRs, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 11:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the first three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as ((Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 11-a:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the first three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as ((Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 11-b:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the first three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as ((Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 11-c:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the first three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as ((Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 11-d:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the first three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as ((Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 11-e:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the first three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as ((Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 11-f:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the first three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as ((Data-Prediction)$/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 12:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the last three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. In the last two $ \cos(\theta^\ast) $ bins (lower row) the resolved and merged categories are combined. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 12-a:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the last three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. In the last two $ \cos(\theta^\ast) $ bins (lower row) the resolved and merged categories are combined. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 12-b:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the last three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. In the last two $ \cos(\theta^\ast) $ bins (lower row) the resolved and merged categories are combined. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 12-c:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the last three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. In the last two $ \cos(\theta^\ast) $ bins (lower row) the resolved and merged categories are combined. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 12-d:
Postfit distributions in $ m_{{\mathrm{t}\overline{\mathrm{t}}} } $ in the single-lepton channel for data and simulation in the last three bins of $ \cos(\theta^\ast) $ in the $ \mathrm{t} \overline{\mathrm{t}} $ SR, shown for the resolved (0 t \text{tag}, left) and merged (1 t \text{tag}, right) categories, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. In the last two $ \cos(\theta^\ast) $ bins (lower row) the resolved and merged categories are combined. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1\unitpb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)/\sigma $, where $ \sigma $ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 13:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation in the CR for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $\sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 13-a:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation in the CR for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $\sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 13-b:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation in the CR for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $\sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 13-c:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation in the CR for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $\sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 14:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation for the resolved (left) and merged (right) categories for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper), $ \mathrm{e}\mu $ (middle), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1 pb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $ \sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
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Figure 14-a:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation for the resolved (left) and merged (right) categories for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper), $ \mathrm{e}\mu $ (middle), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1 pb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $ \sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 14-b:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation for the resolved (left) and merged (right) categories for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper), $ \mathrm{e}\mu $ (middle), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1 pb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $ \sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 14-c:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation for the resolved (left) and merged (right) categories for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper), $ \mathrm{e}\mu $ (middle), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1 pb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $ \sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 14-d:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation for the resolved (left) and merged (right) categories for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper), $ \mathrm{e}\mu $ (middle), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1 pb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $ \sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 14-e:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation for the resolved (left) and merged (right) categories for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper), $ \mathrm{e}\mu $ (middle), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1 pb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $ \sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 14-f:
Postfit distributions in $ S_{\mathrm{T}} $ for data and simulation for the resolved (left) and merged (right) categories for the dilepton channel. Distributions are shown for the $ \mu\mu $ (upper), $ \mathrm{e}\mu $ (middle), and $ \mathrm{e}\mathrm{e} $ (lower) channels, under the background-only hypothesis. The horizontal bars on the data points indicate the bin width. For illustrative purposes, the $ \mathrm{Z}^{'} $ boson signal with a relative width of 1% and a mass of 2 TeV is normalized to a cross section of 1 pb and overlaid to the backgrounds. The lower panels show the pulls, defined as (Data-Prediction)$/\sigma$, where $ \sigma$ denotes the total postfit uncertainty in each bin, relative to the SM prediction. |
png pdf |
Figure 15:
Expected and observed upper limits at 95% CL on the product of the production cross section and branching fraction as functions of the resonance mass. The limits are shown for $ \mathrm{Z}^{'} $ bosons with 1 (upper left), 10 (upper right), and 30% (lower) relative widths. In each panel we plot the expected combined upper limit on the signal strength times branching ratio (black dashed line) together with the 68 (light blue) and 95% (yellow) uncertainty bands, and the corresponding observed upper limit (black solid line). The expected (dashed lines) and observed (solid lines) limits from the single channels are overlaid: all-hadronic (purple), single-lepton (blue), and dilepton (light brown). The limits are compared with the respective theory predictions shown by the solid red curves. The rise in the limits seen at high mass for the $ \mathrm{Z}^{'} $ boson interpretation at 1% relative width (upper left) for the all-hadronic case arises from the limited number of events available to estimate the background. |
png pdf |
Figure 15-a:
Expected and observed upper limits at 95% CL on the product of the production cross section and branching fraction as functions of the resonance mass. The limits are shown for $ \mathrm{Z}^{'} $ bosons with 1 (upper left), 10 (upper right), and 30% (lower) relative widths. In each panel we plot the expected combined upper limit on the signal strength times branching ratio (black dashed line) together with the 68 (light blue) and 95% (yellow) uncertainty bands, and the corresponding observed upper limit (black solid line). The expected (dashed lines) and observed (solid lines) limits from the single channels are overlaid: all-hadronic (purple), single-lepton (blue), and dilepton (light brown). The limits are compared with the respective theory predictions shown by the solid red curves. The rise in the limits seen at high mass for the $ \mathrm{Z}^{'} $ boson interpretation at 1% relative width (upper left) for the all-hadronic case arises from the limited number of events available to estimate the background. |
png pdf |
Figure 15-b:
Expected and observed upper limits at 95% CL on the product of the production cross section and branching fraction as functions of the resonance mass. The limits are shown for $ \mathrm{Z}^{'} $ bosons with 1 (upper left), 10 (upper right), and 30% (lower) relative widths. In each panel we plot the expected combined upper limit on the signal strength times branching ratio (black dashed line) together with the 68 (light blue) and 95% (yellow) uncertainty bands, and the corresponding observed upper limit (black solid line). The expected (dashed lines) and observed (solid lines) limits from the single channels are overlaid: all-hadronic (purple), single-lepton (blue), and dilepton (light brown). The limits are compared with the respective theory predictions shown by the solid red curves. The rise in the limits seen at high mass for the $ \mathrm{Z}^{'} $ boson interpretation at 1% relative width (upper left) for the all-hadronic case arises from the limited number of events available to estimate the background. |
png pdf |
Figure 15-c:
Expected and observed upper limits at 95% CL on the product of the production cross section and branching fraction as functions of the resonance mass. The limits are shown for $ \mathrm{Z}^{'} $ bosons with 1 (upper left), 10 (upper right), and 30% (lower) relative widths. In each panel we plot the expected combined upper limit on the signal strength times branching ratio (black dashed line) together with the 68 (light blue) and 95% (yellow) uncertainty bands, and the corresponding observed upper limit (black solid line). The expected (dashed lines) and observed (solid lines) limits from the single channels are overlaid: all-hadronic (purple), single-lepton (blue), and dilepton (light brown). The limits are compared with the respective theory predictions shown by the solid red curves. The rise in the limits seen at high mass for the $ \mathrm{Z}^{'} $ boson interpretation at 1% relative width (upper left) for the all-hadronic case arises from the limited number of events available to estimate the background. |
png pdf |
Figure 16:
Expected and observed upper limits at 95% CL on the product of the production cross section and branching fraction as functions of the resonance mass. The limits are shown for the Kaluza--Klein gluon (left) and dark matter (right) scenarios. In each panel we plot the expected combined upper limit on the signal strength times branching fraction (black dashed line) together with the 68 (light blue) and 95% (yellow) uncertainty bands, and the corresponding observed upper limit (black solid line). The expected (dashed lines) and observed (solid lines) limits from the individual channels are overlaid: all-hadronic (purple), single-lepton (blue), and dilepton (light brown). The limits are compared with the respective theory predictions shown by the solid red curves. |
png pdf |
Figure 16-a:
Expected and observed upper limits at 95% CL on the product of the production cross section and branching fraction as functions of the resonance mass. The limits are shown for the Kaluza--Klein gluon (left) and dark matter (right) scenarios. In each panel we plot the expected combined upper limit on the signal strength times branching fraction (black dashed line) together with the 68 (light blue) and 95% (yellow) uncertainty bands, and the corresponding observed upper limit (black solid line). The expected (dashed lines) and observed (solid lines) limits from the individual channels are overlaid: all-hadronic (purple), single-lepton (blue), and dilepton (light brown). The limits are compared with the respective theory predictions shown by the solid red curves. |
png pdf |
Figure 16-b:
Expected and observed upper limits at 95% CL on the product of the production cross section and branching fraction as functions of the resonance mass. The limits are shown for the Kaluza--Klein gluon (left) and dark matter (right) scenarios. In each panel we plot the expected combined upper limit on the signal strength times branching fraction (black dashed line) together with the 68 (light blue) and 95% (yellow) uncertainty bands, and the corresponding observed upper limit (black solid line). The expected (dashed lines) and observed (solid lines) limits from the individual channels are overlaid: all-hadronic (purple), single-lepton (blue), and dilepton (light brown). The limits are compared with the respective theory predictions shown by the solid red curves. |
png pdf |
Figure 17:
Expected and observed upper limits at 95% CL on the coupling strength modifier for scalar (H, left) and pseudoscalar ($ \mathrm{A} $, right) heavy Higgs bosons with relative widths of 2.5 (upper), 10 (middle), and 25% (lower), respectively. The solid gray shaded area denotes the parameter space excluded by this search. The discontinuity in the shape of the excluded region, observed for the 25% width pseudoscalar signals with masses below 0.8 TeV, arises from the behavior of the $ \text{CL}_\text{s} $ scan. The gray hatched area indicates the unphysical parameter space where the partial width $ \Gamma_{\Phi{\mathrm{t}\overline{\mathrm{t}}} } $ exceeds the total width $ \Gamma_{\Phi} $. |
png pdf |
Figure 17-a:
Expected and observed upper limits at 95% CL on the coupling strength modifier for scalar (H, left) and pseudoscalar ($ \mathrm{A} $, right) heavy Higgs bosons with relative widths of 2.5 (upper), 10 (middle), and 25% (lower), respectively. The solid gray shaded area denotes the parameter space excluded by this search. The discontinuity in the shape of the excluded region, observed for the 25% width pseudoscalar signals with masses below 0.8 TeV, arises from the behavior of the $ \text{CL}_\text{s} $ scan. The gray hatched area indicates the unphysical parameter space where the partial width $ \Gamma_{\Phi{\mathrm{t}\overline{\mathrm{t}}} } $ exceeds the total width $ \Gamma_{\Phi} $. |
png pdf |
Figure 17-b:
Expected and observed upper limits at 95% CL on the coupling strength modifier for scalar (H, left) and pseudoscalar ($ \mathrm{A} $, right) heavy Higgs bosons with relative widths of 2.5 (upper), 10 (middle), and 25% (lower), respectively. The solid gray shaded area denotes the parameter space excluded by this search. The discontinuity in the shape of the excluded region, observed for the 25% width pseudoscalar signals with masses below 0.8 TeV, arises from the behavior of the $ \text{CL}_\text{s} $ scan. The gray hatched area indicates the unphysical parameter space where the partial width $ \Gamma_{\Phi{\mathrm{t}\overline{\mathrm{t}}} } $ exceeds the total width $ \Gamma_{\Phi} $. |
png pdf |
Figure 17-c:
Expected and observed upper limits at 95% CL on the coupling strength modifier for scalar (H, left) and pseudoscalar ($ \mathrm{A} $, right) heavy Higgs bosons with relative widths of 2.5 (upper), 10 (middle), and 25% (lower), respectively. The solid gray shaded area denotes the parameter space excluded by this search. The discontinuity in the shape of the excluded region, observed for the 25% width pseudoscalar signals with masses below 0.8 TeV, arises from the behavior of the $ \text{CL}_\text{s} $ scan. The gray hatched area indicates the unphysical parameter space where the partial width $ \Gamma_{\Phi{\mathrm{t}\overline{\mathrm{t}}} } $ exceeds the total width $ \Gamma_{\Phi} $. |
png pdf |
Figure 17-d:
Expected and observed upper limits at 95% CL on the coupling strength modifier for scalar (H, left) and pseudoscalar ($ \mathrm{A} $, right) heavy Higgs bosons with relative widths of 2.5 (upper), 10 (middle), and 25% (lower), respectively. The solid gray shaded area denotes the parameter space excluded by this search. The discontinuity in the shape of the excluded region, observed for the 25% width pseudoscalar signals with masses below 0.8 TeV, arises from the behavior of the $ \text{CL}_\text{s} $ scan. The gray hatched area indicates the unphysical parameter space where the partial width $ \Gamma_{\Phi{\mathrm{t}\overline{\mathrm{t}}} } $ exceeds the total width $ \Gamma_{\Phi} $. |
png pdf |
Figure 17-e:
Expected and observed upper limits at 95% CL on the coupling strength modifier for scalar (H, left) and pseudoscalar ($ \mathrm{A} $, right) heavy Higgs bosons with relative widths of 2.5 (upper), 10 (middle), and 25% (lower), respectively. The solid gray shaded area denotes the parameter space excluded by this search. The discontinuity in the shape of the excluded region, observed for the 25% width pseudoscalar signals with masses below 0.8 TeV, arises from the behavior of the $ \text{CL}_\text{s} $ scan. The gray hatched area indicates the unphysical parameter space where the partial width $ \Gamma_{\Phi{\mathrm{t}\overline{\mathrm{t}}} } $ exceeds the total width $ \Gamma_{\Phi} $. |
png pdf |
Figure 17-f:
Expected and observed upper limits at 95% CL on the coupling strength modifier for scalar (H, left) and pseudoscalar ($ \mathrm{A} $, right) heavy Higgs bosons with relative widths of 2.5 (upper), 10 (middle), and 25% (lower), respectively. The solid gray shaded area denotes the parameter space excluded by this search. The discontinuity in the shape of the excluded region, observed for the 25% width pseudoscalar signals with masses below 0.8 TeV, arises from the behavior of the $ \text{CL}_\text{s} $ scan. The gray hatched area indicates the unphysical parameter space where the partial width $ \Gamma_{\Phi{\mathrm{t}\overline{\mathrm{t}}} } $ exceeds the total width $ \Gamma_{\Phi} $. |
| Tables | |
png pdf |
Table 1:
Sources of systematic uncertainties and correlations between them. The correlations take various forms: among data-taking years, among different processes (such as $ \mathrm{t} \overline{\mathrm{t}} $, single top quark production, etc), and/or channels (0\ell, 1\ell, and 2\ell). The $ \mathrm{Z}^{'} $ signal with a relative width of 1% and a mass of 2 TeV is used as a benchmark. The `` $ \mathrm{t} \overline{\mathrm{t}} $ rate'' row corresponds to the overall prior uncertainty in the $ \mathrm{t} \overline{\mathrm{t}} $ production cross section. The `` $ \mathrm{t} \overline{\mathrm{t}} $ shape'' row corresponds to differences in shapes between the NLO simulation and measured values of the $ \mathrm{t} \overline{\mathrm{t}} $ $ p_{\mathrm{T}} $ spectrum at large momentum due to destructive interference from higher-order terms that are not present in the simulation. |
png pdf |
Table 2:
Relative contribution of the dominant sources of uncertainty to the total variance of the upper limits. The benchmark scenario corresponds to a $ \mathrm{Z}^{'} $ signal with a 1% relative width and a mass of 2 TeV. The top-quark modeling category includes nuisance parameters associated with the $ \mathrm{t} \overline{\mathrm{t}} $ production rate, $ \mathrm{t}\text{ tagging} $ efficiency, $ \mathrm{t}\text{ tagging} $ mistag rate, and modeling of the $ \mathrm{t} \overline{\mathrm{t}} $ transverse momentum spectrum. |
| Summary |
| A search for new particles decaying to a top quark-antiquark pair has been presented. The analysis uses 138 fb$ ^{-1} $ of data collected during 2016--2018 by the CMS experiment at a centre-of-mass energy of 13 TeV. The analysis performs a model-independent search and is sensitive both to the resolved and the merged regimes of the top quark hadronic decay. Upper limits at 95% confidence level are placed for different benchmark models. Heavy $ \mathrm{Z}^{'} $ bosons in the leptophobic topcolor model with relative widths of 1, 10, and 30% are excluded for mass ranges 0.4--4.8, 0.4--6.2, and 0.4--7.4 TeV, respectively. Additionally, Kaluza--Klein gluons in the Randall--Sundrum model and dark-matter mediators are excluded for masses between 0.5--5.5 and 1.0--4.2 TeV, respectively. These results set the most stringent limits to date for the considered models. Limits on the coupling strength modifier are set for scalar and pseudoscalar heavy Higgs bosons in two-Higgs-doublet models for 2.5, 10, and 25% relative widths in the mass range 0.5--1 TeV. |
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