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| CMS-PAS-TOP-24-006 | ||
| Search for three-top-quark production in the single lepton, same-sign dilepton, and multilepton final states in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 2026-03-31 | ||
| Abstract: A search for the standard model production of three top quarks is presented. The data analyzed were collected with the CMS detector at the CERN LHC in proton-proton collisions at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 138 fb$ ^{-1} $. Selected events are required to contain jets and either one lepton (electron or muon), two same-sign charged leptons, or at least three leptons. The results are derived from the combination of these three lepton categories. Novel multivariate techniques are employed to take full advantage of kinematic differences between the studied signal and the major background. This analysis provides the first LHC result specifically targeting three-top-quark production. No significant deviations with respect to the standard model predictions are observed, and an upper limit of 25 $ \mathrm{fb} $ is set on the signal cross section at 95% confidence level. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Principal Feynman diagrams at LO for SM three-top-quark production in the $ t $ channel (left), in association with a W boson (center), and via the $ s $ channel (right). |
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Figure 2:
Distributions of the DNN score for uncorrected simulated $ \mathrm{t} \overline{\mathrm{t}} $ events (green), the observed data (black markers), and the ABCDnn-corrected prediction (blue) for events with $ N_{\text{HOT}}\geq $ 1 from the 2018 data set. Distributions in the upper, middle, and lower rows are shown for events with four, five, and at least six jets, respectively, whereas the left and right columns differ in the number of b-tagged jets (one and at least two, respectively). The lower panels show the ratio and statistical error of data to $ \mathrm{t} \overline{\mathrm{t}} $ simulation before and after the ABCDnn model is applied. |
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Figure 3:
Transverse energy $ H_{\mathrm{T}} $ distributions validating the estimation of the nonprompt-lepton background. The distributions are separated by lepton flavor: $ \mathrm{e}\mathrm{e} $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mu\mu $ (lower). |
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Figure 3-a:
Transverse energy $ H_{\mathrm{T}} $ distributions validating the estimation of the nonprompt-lepton background. The distributions are separated by lepton flavor: $ \mathrm{e}\mathrm{e} $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mu\mu $ (lower). |
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Figure 3-b:
Transverse energy $ H_{\mathrm{T}} $ distributions validating the estimation of the nonprompt-lepton background. The distributions are separated by lepton flavor: $ \mathrm{e}\mathrm{e} $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mu\mu $ (lower). |
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Figure 3-c:
Transverse energy $ H_{\mathrm{T}} $ distributions validating the estimation of the nonprompt-lepton background. The distributions are separated by lepton flavor: $ \mathrm{e}\mathrm{e} $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mu\mu $ (lower). |
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Figure 4:
Distributions of the lepton $ \eta $ (left) and $ p_{\mathrm{T}} $ (right) showing the closure of the electron charge misidentification rate. |
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Figure 4-a:
Distributions of the lepton $ \eta $ (left) and $ p_{\mathrm{T}} $ (right) showing the closure of the electron charge misidentification rate. |
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Figure 4-b:
Distributions of the lepton $ \eta $ (left) and $ p_{\mathrm{T}} $ (right) showing the closure of the electron charge misidentification rate. |
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Figure 5:
Distributions of the four-top-quark BDT score after training with normalized distributions for $ \mathrm{t}\mathrm{t}\mathrm{t} $, $ {\mathrm{t}\overline{\mathrm{t}}} {\mathrm{t}\overline{\mathrm{t}}} $, and the other standard model backgrounds. |
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Figure 6:
Distribution of the DNN score in the SL channel in the signal regions with $ N_{\text{HOT}}= $ 0 (left column) or $ N_{\text{HOT}}\geq $ 1 (right column) in the electron channel (upper row) and muon channel (lower row) after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 6-a:
Distribution of the DNN score in the SL channel in the signal regions with $ N_{\text{HOT}}= $ 0 (left column) or $ N_{\text{HOT}}\geq $ 1 (right column) in the electron channel (upper row) and muon channel (lower row) after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 6-b:
Distribution of the DNN score in the SL channel in the signal regions with $ N_{\text{HOT}}= $ 0 (left column) or $ N_{\text{HOT}}\geq $ 1 (right column) in the electron channel (upper row) and muon channel (lower row) after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 6-c:
Distribution of the DNN score in the SL channel in the signal regions with $ N_{\text{HOT}}= $ 0 (left column) or $ N_{\text{HOT}}\geq $ 1 (right column) in the electron channel (upper row) and muon channel (lower row) after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 6-d:
Distribution of the DNN score in the SL channel in the signal regions with $ N_{\text{HOT}}= $ 0 (left column) or $ N_{\text{HOT}}\geq $ 1 (right column) in the electron channel (upper row) and muon channel (lower row) after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 7:
The SSDL and ML discriminant distributions in the SSDL region (upper left), ML region (upper right), four-top-quark control region (lower left), and $ tt\mathrm{Z} $ control region (lower right), after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 7-a:
The SSDL and ML discriminant distributions in the SSDL region (upper left), ML region (upper right), four-top-quark control region (lower left), and $ tt\mathrm{Z} $ control region (lower right), after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 7-b:
The SSDL and ML discriminant distributions in the SSDL region (upper left), ML region (upper right), four-top-quark control region (lower left), and $ tt\mathrm{Z} $ control region (lower right), after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 7-c:
The SSDL and ML discriminant distributions in the SSDL region (upper left), ML region (upper right), four-top-quark control region (lower left), and $ tt\mathrm{Z} $ control region (lower right), after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 7-d:
The SSDL and ML discriminant distributions in the SSDL region (upper left), ML region (upper right), four-top-quark control region (lower left), and $ tt\mathrm{Z} $ control region (lower right), after a signal-plus-background fit across all channels. The solid histograms for the simulated SM backgrounds are stacked, while the four-top-quark process and the three-top-quark signal distributions are overlaid. The grey shaded area in the upper and lower panels represents the total uncertainty in the sum of the SM backgrounds and signal. The data are represented by black markers with the vertical bar indicating the associated statistical uncertainty. The last bin contains overflow events. The lower panels show the ratio of data and the postfit SM background. |
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Figure 8:
Upper limits at 95% CL for $ \sigma_{\mathrm{t}\mathrm{t}\mathrm{t}} $ for each channel and their combination. The observed (expected) limits are shown as a solid (dashed) black line and the inner (green) band and the outer (yellow) band indicate the regions containing 68% and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
| Tables | |
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Table 1:
Observed and expected upper limits at 95% CL on $ \sigma_{\mathrm{t}\mathrm{t}\mathrm{t}} $ for each channel and their combination. |
| Summary |
| A search for standard model three-top-quark ($ \mathrm{t}\mathrm{t}\mathrm{t} $) production in proton-proton collisions at a center-of-mass energy of 13 TeV has been presented. The analysis was performed using data corresponding to an integrated luminosity of 138 fb$ ^{-1} $ recorded by the CMS experiment between 2016 and 2018. This note presents the first dedicated analysis of $ \mathrm{t}\mathrm{t}\mathrm{t} $ production at the LHC. The final states were categorized by the number and charge of prompt electrons and muons, which can be produced from leptonic W boson decays. The single lepton, same-sign dilepton, and multilepton final states were considered. Several new strategies were introduced to mitigate the impact of the dominant or poorly modeled backgrounds, including machine-learning-driven background estimation methods utilizing data in background-enriched control regions. Optimized multivariate methods were also employed to discriminate between the dominant backgrounds and the three-top-quark signal. An observed upper limit of 25$ \text{fb}$ is set on the $ \mathrm{t}\mathrm{t}\mathrm{t} $ cross section at 95% confidence level. |
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