Abstract

A search for the production of top-quark pairs with the same electric charge ($tt$ or $\bar{t}\bar{t}$) is presented. The analysis uses proton-proton collision data at $\sqrt{s}=13$ TeV, recorded by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb$^{-1}$. Events with two same-charge leptons and at least two $b$-tagged jets are selected. Neural networks are employed to define two selections sensitive to additional couplings beyond the Standard Model that would enhance the production rate of same-sign top-quark pairs. No significant signal is observed, leading to an upper limit on the total production cross-section of same-sign top-quark pairs of 1.6 fb at 95$\%$ confidence level. Corresponding limits on the three Wilson coefficients associated with the ${\cal O}_{tu}^{(1)}$, ${\cal O}_{Qu}^{(1)}$, and ${\cal O}_{Qu}^{(8)}$ operators in the Standard Model Effective Field Theory framework are derived.

Figure 6 top left

Data from Figure 6 (top left)

10.17182/hepdata.155341.v1/t1

Distributions of the $\mathrm{NN^{SvsB}}$ output for data and the expected background after the likelihood fit in the $SR_{ctu ++}$ signal...
Figure 6 top right

Data from Figure 6 (top right)

10.17182/hepdata.155341.v1/t2

Distributions of the $\mathrm{NN^{SvsB}}$ output for data and the expected background after the likelihood fit in the $SR_{ctu --}$ signal...
Figure 6 bottom left

Data from Figure 6 (bottom left)

10.17182/hepdata.155341.v1/t3

Distributions of the $\mathrm{NN^{SvsB}}$ output for data and the expected background after the likelihood fit in the $SR_{cQu ++}$ signal...
Figure 6 bottom right

Data from Figure 6 (bottom right)

10.17182/hepdata.155341.v1/t4

Distributions of the $\mathrm{NN^{SvsB}}$ output for data and the expected background after the likelihood fit in the $SR_{cQu --}$ signal...
Table 3

Data from Table 3

10.17182/hepdata.155341.v1/t5

Summary of the observed and predicted number of events in the five 2$\ell$ control regions. The background prediction is shown...
Table 4

Data from Table 4

10.17182/hepdata.155341.v1/t6

Summary of the observed and predicted number of events in the four 3$\ell$ control regions. The background prediction is shown...
Figure 7

Data from Figure 7

10.17182/hepdata.155341.v1/t7

Comparison of the observed limits on the three WCs to the limit obtained by the ATLAS Run~1 analysis of events...
Figure 8

Data from Figure 8

10.17182/hepdata.155341.v1/t8

Observed lower limits at 95$\%$ confidence level on the scale of new physics $\Lambda$ for Wilson coefficient values of 0.01,...
Cross-section limit on $\sigma(pp \rightarrow tt)$

Conclusion & Result section

10.17182/hepdata.155341.v1/t9

Observed and expected limits at 95$\%$ confidence level on the cross-section of $\sigma(pp \rightarrow tt)$.
Figure 9(a)

Data from Figure 9(a) (top left)

10.17182/hepdata.155341.v1/t10

2D likelihood scans of the Wilson coefficients $c_{tu}^{(1)}$ versus $c_{Qu}^{(1)}$. The new-physics scale is set to $\Lambda = 1 \,...
Figure 9(b)

Data from Figure 9(b) (top right)

10.17182/hepdata.155341.v1/t11

2D likelihood scans of the Wilson coefficients $c_{tu}^{(1)}$ versus $c_{Qu}^{(8)}$. The new-physics scale is set to $\Lambda = 1 \,...
Figure 9(c)

Data from Figure 9(c) (bottom)

10.17182/hepdata.155341.v1/t12

2D likelihood scans of the Wilson coefficients $c_{Qu}^{(1)}$ versus $c_{Qu}^{(8)}$. The new-physics scale is set to $\Lambda = 1 \,...
Figure 01a (Auxiliary material)

Data from Figure 01a (Auxiliary material)

10.17182/hepdata.155341.v1/t13

1D-likelihood scan for $c_{tu}^{(1)}$. The observed and expected limits at 68\% and 95\% confidence level (CL) can be read off...
Figure 01b (Auxiliary material)

Data from Figure 01b (Auxiliary material)

10.17182/hepdata.155341.v1/t14

1D-likelihood scan for $c_{Qu}^{(1)}$. The observed and expected limits at 68\% and 95\% confidence level (CL) can be read off...
Figure 01c (Auxiliary material)

Data from Figure 01c (Auxiliary material)

10.17182/hepdata.155341.v1/t15

1D-likelihood scan for $c_{Qu}^{(8)}$. The observed and expected limits at 68\% and 95\% confidence level (CL) can be read off...

Figure 6 top left

Figure 6 top right

Figure 6 bottom left

Figure 6 bottom right

Table 3

Table 4

Figure 7

Figure 8

Cross-section limit on $\sigma(pp \rightarrow tt)$

Figure 9(a)

Figure 9(b)

Figure 9(c)

Figure 01a (Auxiliary material)

Figure 01b (Auxiliary material)

Figure 01c (Auxiliary material)

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