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| CMS-PAS-B2G-24-003 | ||
| Search for $ \mathrm{t}\overline{\mathrm{t}} $ resonances in the fully hadronic final state | ||
| CMS Collaboration | ||
| 2 April 2025 | ||
| Abstract: A search for a heavy resonance decaying into a top quark-antiquark pair is presented, using 138 fb$ ^{-1} $ of proton-proton collision data collected at $ \sqrt{s}= $ 13 TeV with the Compact Muon Solenoid (CMS) detector. This analysis employs machine-learning-based techniques for top quark identification in the fully hadronic decay channel and achieves improved sensitivity compared to previous searches. The search is optimized for highly Lorentz-boosted top quark decays, where the hadronic decay products are reconstructed as a single merged jet. Upper limits are set on the production cross section of a leptophobic topcolor $ Z' $ resonance with widths of 1%, 10%, and 30% of the resonance mass. These widths are chosen to cover a range of theoretically motivated models, enabling reinterpretation of the results. The corresponding lower mass limits for these benchmark scenarios are 4.49, 5.52, and 6.85 TeV, respectively. Additionally, two specific models are considered: a Kaluza-Klein excitation of the gluon in the Randall-Sundrum model, excluded up to 5.0 TeV, and a dark matter model with a massive mediator coupling to top quarks, excluded up to 3.9 TeV. These results represent the most stringent limits in this channel to date, particularly in the high-mass regime starting from 3 TeV. | ||
| Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Production of Z' particles decaying into a $ {\mathrm{t}\overline{\mathrm{t}}} $ pair, which subsequently decays hadronically. |
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Figure 2:
Run 2 data-to-MC comparison of distributions for the top mass of the leading jet (left) and the reconstructed $ {\mathrm{t}\overline{\mathrm{t}}} $ mass (right) in the inclusive central and forward categories, where both jets pass the top-tagging SR requirement. |
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Figure 2-a:
Run 2 data-to-MC comparison of distributions for the top mass of the leading jet (left) and the reconstructed $ {\mathrm{t}\overline{\mathrm{t}}} $ mass (right) in the inclusive central and forward categories, where both jets pass the top-tagging SR requirement. |
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Figure 2-b:
Run 2 data-to-MC comparison of distributions for the top mass of the leading jet (left) and the reconstructed $ {\mathrm{t}\overline{\mathrm{t}}} $ mass (right) in the inclusive central and forward categories, where both jets pass the top-tagging SR requirement. |
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Figure 3:
Signal distributions for Z' with 1% and 30% widths shown in the left and right panels, respectively. Signal lines correspond to Z' masses of 2, 4, and 6 TeV where both jets pass the top-tagging SR requirement. Signal events are normalized to 1 pb. |
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Figure 3-a:
Signal distributions for Z' with 1% and 30% widths shown in the left and right panels, respectively. Signal lines correspond to Z' masses of 2, 4, and 6 TeV where both jets pass the top-tagging SR requirement. Signal events are normalized to 1 pb. |
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Figure 3-b:
Signal distributions for Z' with 1% and 30% widths shown in the left and right panels, respectively. Signal lines correspond to Z' masses of 2, 4, and 6 TeV where both jets pass the top-tagging SR requirement. Signal events are normalized to 1 pb. |
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Figure 4:
Illustration of the background estimation method. The dataset is separated into regions that pass and fail the subleading jet t-tagging requirement, as well as regions in the leading jet mass $ m_\mathrm{t} $ above and below the top quark mass window. A two-dimensional polynomial fit is used to estimate the QCD background in Region E from Regions A, B, C, D, and F. |
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Figure 5:
Post-fit $ {\mathrm{t}\overline{\mathrm{t}}} $ mass distribution in the $ m_\mathrm{t} $ sidebands after QCD background estimation, using the combined Run 2 dataset. The top panel corresponds to the central category, while the bottom panel corresponds to the forward category. Distributions are shown for the low $ m_\mathrm{t} $ (left) and high $ m_\mathrm{t} $ (right) sidebands. The lower part of each distribution shows the pull, defined as (Data-Bkg)/$ \sigma $, where $ \sigma $ denotes the total uncertainty. |
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Figure 5-a:
Post-fit $ {\mathrm{t}\overline{\mathrm{t}}} $ mass distribution in the $ m_\mathrm{t} $ sidebands after QCD background estimation, using the combined Run 2 dataset. The top panel corresponds to the central category, while the bottom panel corresponds to the forward category. Distributions are shown for the low $ m_\mathrm{t} $ (left) and high $ m_\mathrm{t} $ (right) sidebands. The lower part of each distribution shows the pull, defined as (Data-Bkg)/$ \sigma $, where $ \sigma $ denotes the total uncertainty. |
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Figure 5-b:
Post-fit $ {\mathrm{t}\overline{\mathrm{t}}} $ mass distribution in the $ m_\mathrm{t} $ sidebands after QCD background estimation, using the combined Run 2 dataset. The top panel corresponds to the central category, while the bottom panel corresponds to the forward category. Distributions are shown for the low $ m_\mathrm{t} $ (left) and high $ m_\mathrm{t} $ (right) sidebands. The lower part of each distribution shows the pull, defined as (Data-Bkg)/$ \sigma $, where $ \sigma $ denotes the total uncertainty. |
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Figure 5-c:
Post-fit $ {\mathrm{t}\overline{\mathrm{t}}} $ mass distribution in the $ m_\mathrm{t} $ sidebands after QCD background estimation, using the combined Run 2 dataset. The top panel corresponds to the central category, while the bottom panel corresponds to the forward category. Distributions are shown for the low $ m_\mathrm{t} $ (left) and high $ m_\mathrm{t} $ (right) sidebands. The lower part of each distribution shows the pull, defined as (Data-Bkg)/$ \sigma $, where $ \sigma $ denotes the total uncertainty. |
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Figure 5-d:
Post-fit $ {\mathrm{t}\overline{\mathrm{t}}} $ mass distribution in the $ m_\mathrm{t} $ sidebands after QCD background estimation, using the combined Run 2 dataset. The top panel corresponds to the central category, while the bottom panel corresponds to the forward category. Distributions are shown for the low $ m_\mathrm{t} $ (left) and high $ m_\mathrm{t} $ (right) sidebands. The lower part of each distribution shows the pull, defined as (Data-Bkg)/$ \sigma $, where $ \sigma $ denotes the total uncertainty. |
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Figure 6:
Post-fit $ {\mathrm{t}\overline{\mathrm{t}}} $ mass distribution in the signal region after QCD background estimation, using the combined Run 2 dataset. The left panel corresponds to the central category, while the right panel corresponds to the forward category. The lower part of each distribution shows the pull, defined as (Data-Bkg)/$ \sigma $, where $ \sigma $ denotes the total uncertainty. Signal distributions are scaled to 0.5 pb for visualization purposes. |
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Figure 6-a:
Post-fit $ {\mathrm{t}\overline{\mathrm{t}}} $ mass distribution in the signal region after QCD background estimation, using the combined Run 2 dataset. The left panel corresponds to the central category, while the right panel corresponds to the forward category. The lower part of each distribution shows the pull, defined as (Data-Bkg)/$ \sigma $, where $ \sigma $ denotes the total uncertainty. Signal distributions are scaled to 0.5 pb for visualization purposes. |
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Figure 6-b:
Post-fit $ {\mathrm{t}\overline{\mathrm{t}}} $ mass distribution in the signal region after QCD background estimation, using the combined Run 2 dataset. The left panel corresponds to the central category, while the right panel corresponds to the forward category. The lower part of each distribution shows the pull, defined as (Data-Bkg)/$ \sigma $, where $ \sigma $ denotes the total uncertainty. Signal distributions are scaled to 0.5 pb for visualization purposes. |
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Figure 7:
Expected and observed 95% CL upper limits on the cross section times branching ratio for five signal scenarios with three different width hypotheses: 1%, 10%, and 30%, as well as $ Z_{DM} $ and $ g_{KK} $, as a function of the new heavy particle mass. The five models considered are: a Z' boson with a width of 1% of its mass (upper left), a Z' boson with a width of 10% (upper right), a Z' boson with a width of 30% (lower left), $ Z_{DM} $ (lower right), and an RS KK gluon (bottom). The dashed black line represents the median expected limit, while the solid black line denotes the observed limit. The green (yellow) bands correspond to the one (two) sigma expected limit deviations. The solid red line shows the theoretical cross section expected for the signal process of interest. |
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Figure 7-a:
Expected and observed 95% CL upper limits on the cross section times branching ratio for five signal scenarios with three different width hypotheses: 1%, 10%, and 30%, as well as $ Z_{DM} $ and $ g_{KK} $, as a function of the new heavy particle mass. The five models considered are: a Z' boson with a width of 1% of its mass (upper left), a Z' boson with a width of 10% (upper right), a Z' boson with a width of 30% (lower left), $ Z_{DM} $ (lower right), and an RS KK gluon (bottom). The dashed black line represents the median expected limit, while the solid black line denotes the observed limit. The green (yellow) bands correspond to the one (two) sigma expected limit deviations. The solid red line shows the theoretical cross section expected for the signal process of interest. |
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Figure 7-b:
Expected and observed 95% CL upper limits on the cross section times branching ratio for five signal scenarios with three different width hypotheses: 1%, 10%, and 30%, as well as $ Z_{DM} $ and $ g_{KK} $, as a function of the new heavy particle mass. The five models considered are: a Z' boson with a width of 1% of its mass (upper left), a Z' boson with a width of 10% (upper right), a Z' boson with a width of 30% (lower left), $ Z_{DM} $ (lower right), and an RS KK gluon (bottom). The dashed black line represents the median expected limit, while the solid black line denotes the observed limit. The green (yellow) bands correspond to the one (two) sigma expected limit deviations. The solid red line shows the theoretical cross section expected for the signal process of interest. |
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Figure 7-c:
Expected and observed 95% CL upper limits on the cross section times branching ratio for five signal scenarios with three different width hypotheses: 1%, 10%, and 30%, as well as $ Z_{DM} $ and $ g_{KK} $, as a function of the new heavy particle mass. The five models considered are: a Z' boson with a width of 1% of its mass (upper left), a Z' boson with a width of 10% (upper right), a Z' boson with a width of 30% (lower left), $ Z_{DM} $ (lower right), and an RS KK gluon (bottom). The dashed black line represents the median expected limit, while the solid black line denotes the observed limit. The green (yellow) bands correspond to the one (two) sigma expected limit deviations. The solid red line shows the theoretical cross section expected for the signal process of interest. |
png pdf |
Figure 7-d:
Expected and observed 95% CL upper limits on the cross section times branching ratio for five signal scenarios with three different width hypotheses: 1%, 10%, and 30%, as well as $ Z_{DM} $ and $ g_{KK} $, as a function of the new heavy particle mass. The five models considered are: a Z' boson with a width of 1% of its mass (upper left), a Z' boson with a width of 10% (upper right), a Z' boson with a width of 30% (lower left), $ Z_{DM} $ (lower right), and an RS KK gluon (bottom). The dashed black line represents the median expected limit, while the solid black line denotes the observed limit. The green (yellow) bands correspond to the one (two) sigma expected limit deviations. The solid red line shows the theoretical cross section expected for the signal process of interest. |
png pdf |
Figure 7-e:
Expected and observed 95% CL upper limits on the cross section times branching ratio for five signal scenarios with three different width hypotheses: 1%, 10%, and 30%, as well as $ Z_{DM} $ and $ g_{KK} $, as a function of the new heavy particle mass. The five models considered are: a Z' boson with a width of 1% of its mass (upper left), a Z' boson with a width of 10% (upper right), a Z' boson with a width of 30% (lower left), $ Z_{DM} $ (lower right), and an RS KK gluon (bottom). The dashed black line represents the median expected limit, while the solid black line denotes the observed limit. The green (yellow) bands correspond to the one (two) sigma expected limit deviations. The solid red line shows the theoretical cross section expected for the signal process of interest. |
| Tables | |
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Table 1:
Summary of systematic uncertainty types for this analysis for SM $ \mathrm{t} \overline{\mathrm{t}} $. All uncertainties listed in the table are applied to the signal as well, except for the $ \mathrm{t} \overline{\mathrm{t}} $ cross section uncertainty, which is only relevant to the SM $ \mathrm{t} \overline{\mathrm{t}} $ background. The $ \mathrm{t} \overline{\mathrm{t}} $ cross section uncertainty is set to a large pre-fit value (30%) and extracted after the fit, and is conservatively separated from the $ Q^2 $ uncertainty. Scale factors for t-tagging are separated by year and $ p_{\mathrm{T}} $. Jet energy scale and resolution are separated by year, $ p_{\mathrm{T}} $, and $ \eta $. Luminosity uncertainties are correlated as indicated in the table. |
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Table 2:
Observed Run 2 mass limits for a Z' boson with a width of 1%, 10% and 30% as well as $ Z_{DM} $ and RS KK gluon |
| Summary |
| A search has been presented for anomalous production of $ {\mathrm{t}\overline{\mathrm{t}}} $ events from resonant signals beyond the standard model. This analysis uses a data-driven background estimate for the QCD multijet background, as well as a simultaneous fit for the standard model $ {\mathrm{t}\overline{\mathrm{t}}} $ cross section and signal. A Kaluza-Klein gluon decaying to top quark pairs is excluded below 5 TeV; a $ Z' $ dark matter mediator is excluded below 3.9 TeV; and sequential standard model $ Z' $ bosons are excluded for 1%, 10%, and 30% relative widths below 4.49, 5.52, and 6.85 TeV, respectively. These constitute the most stringent limits in this channel to date, particularly in the high-mass regime above 3 TeV. |
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Compact Muon Solenoid LHC, CERN |
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