Abstract (data abstract)

A measurment is presented for four-top-quark production using an integrated luminosity of 140 fb$^{-1}$ of proton--proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The four-top-quark production cross section is measured to be $22.5^{+6.6}_{-5.5}$ fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 6.1 (4.3) standard deviations and provides evidence for this process.

Figure 2a: CR ttW+jets (+)

Data from Figure 2a

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Post-fit distributions for the number of jets ($N_{j}$) in CR $t\bar{t}W^{+}$+jets. The QmisID represents the backgrounds with a mis-assigned charge....
Figure 2b: CR ttW+jets (-)

Data from Figure 2b

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Post-fit distributions for the number of jets ($N_{j}$) in CR $t\bar{t}W^{-}$+jets. The QmisID represents the backgrounds with a mis-assigned charge....
Figure 2c: CR 1b(+)

Data from Figure 2c

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Post-fit distributions for the number of jets ($N_{j}$) in CR 1b(+). The QmisID represents the backgrounds with a mis-assigned charge....
Figure 2d: CR 1b(-)

Data from Figure 2d

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Post-fit distributions for the number of jets ($N_{j}$) in CR 1b(-). The QmisID represents the backgrounds with a mis-assigned charge....
Figure 3: ttW validation

Data from Figure 3

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Post-fit distribution for the difference between the number of positive events and the number of negative events ($N_{+}-N_{-}$) as a...
Figure 4a: CR HF e

Data from Figure 4a

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Post-fit distributions for the fitted variables in the CRs for the fake/non-prompt lepton background - CR HF e. The QmisID...
Figure 4b: CR HF mu

Data from Figure 4b

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Post-fit distributions for the fitted variables in the CRs for the fake/non-prompt lepton background - CR HF $\mu$. The QmisID...
Figure 4c: CR Mat. Conv.

Data from Figure 4c

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Post-fit distributions for the fitted variables in the CRs for the fake/non-prompt lepton background - CR Mat. Conv.. The QmisID...
Figure 4d: CR Low m_{gamma*}

Data from Figure 4d

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Post-fit distributions for the fitted variables in the CRs for the fake/non-prompt lepton background - CR Low $m_{\gamma*}$. The QmisID...
Figure 5: GNN in SR

Data from Figure 5

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Comparison between data and the predictions after a fit to data for the GNN distribution in the SR. The QmisID...
Figure 6a: number of jets in GNN >= 0.6

Data from Figure 6a

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Comparison between data and prediction after the fit to data in the signal-enriched region with GNN >= 0.6 for the...
Figure 6b: number of b-jets in GNN >= 0.6

Data from Figure 6b

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Comparison between data and prediction after the fit to data in the signal-enriched region with GNN >= 0.6 for the...
Figure 6c: Leading four PCBT scores of jets (GNN >= 0.6)

Data from Figure 6c

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Comparison between data and prediction after the fit to data in the signal-enriched region with GNN >= 0.6 for the...
Figure 6d: HT (GNN >= 0.6)

Data from Figure 6d

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Comparison between data and prediction after the fit to data in the signal-enriched region with GNN >= 0.6 for the...
Figure 7: NLL contour of ttt and tttt cross sections

Data from Figure 7

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Two-dimensional negative log-likelihood contour for the $t\bar{t}t$ cross section ($\sigma_{t\bar{t}t}$) versus the $t\bar{t}t\bar{t}$ cross section ($\sigma_{t\bar{t}t\bar{t}}$) when the normalisation of...
Figure 9: NLL values of Higgs oblique parameter

Data from Figure 9

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The negative log-likelihood values as a function of the Higgs oblique parameter $\hat{H}$.
The measured and expected cross-sections of tttt production.

Auxiliary data

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The measured and expected cross-sections of $t\bar{t}t\bar{t}$ production.
Figure 8: Observed 68% CL Lower Limit Contour

Data from Figure 8

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Observed 68% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...
Figure 8: Observed 68% CL Upper Limit Contour

Data from Figure 8

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Observed 68% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...
Figure 8: Observed 95% CL Limit Contour

Data from Figure 8

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Observed 95% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...
Figure 8: Expected 68% CL Limit Contour

Data from Figure 8

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Expected 68% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...
Figure 8: Expected 95% CL Limit Contour

Data from Figure 8

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Expected 95% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...
Auxiliary Figure 7: Observed 68% CL Lower Limit Contour

Auxiliary Figure 7

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Observed 68% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...
Auxiliary Figure 7: Observed 68% CL Upper Limit Contour

Auxiliary Figure 7

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Observed 68% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...
Auxiliary Figure 7: Observed 95% CL Limit Contour

Auxiliary Figure 7

10.17182/hepdata.140801.v1/t25

Observed 95% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...
Auxiliary Figure 7: Expected 68% CL Limit Contour

Auxiliary Figure 7

10.17182/hepdata.140801.v1/t26

Expected 68% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...
Auxiliary Figure 7: Expected 95% CL Limit Contour

Auxiliary Figure 7

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Expected 95% CL Limit Contour in $\kappa_t,\alpha$ with $t\bar tt\bar t$ parameterized as a function of $\kappa_t,\alpha$, and the $t\bar...

Figure 2a: CR ttW+jets (+)

Figure 2b: CR ttW+jets (-)

Figure 2c: CR 1b(+)

Figure 2d: CR 1b(-)

Figure 3: ttW validation

Figure 4a: CR HF e

Figure 4b: CR HF mu

Figure 4c: CR Mat. Conv.

Figure 4d: CR Low m_{gamma*}

Figure 5: GNN in SR

Figure 6a: number of jets in GNN >= 0.6

Figure 6b: number of b-jets in GNN >= 0.6

Figure 6c: Leading four PCBT scores of jets (GNN >= 0.6)

Figure 6d: HT (GNN >= 0.6)

Figure 7: NLL contour of ttt and tttt cross sections

Figure 9: NLL values of Higgs oblique parameter

The measured and expected cross-sections of tttt production.

Figure 8: Observed 68% CL Lower Limit Contour

Figure 8: Observed 68% CL Upper Limit Contour

Figure 8: Observed 95% CL Limit Contour

Figure 8: Expected 68% CL Limit Contour

Figure 8: Expected 95% CL Limit Contour

Auxiliary Figure 7: Observed 68% CL Lower Limit Contour

Auxiliary Figure 7: Observed 68% CL Upper Limit Contour

Auxiliary Figure 7: Observed 95% CL Limit Contour

Auxiliary Figure 7: Expected 68% CL Limit Contour

Auxiliary Figure 7: Expected 95% CL Limit Contour

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