Search for same-charge top-quark pair production in $pp$ collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector

TL;DR

This paper reports a search for same-charge top-quark pair production in proton-proton collisions at 13 TeV using the ATLAS detector, employing neural networks to enhance sensitivity and setting limits on production cross-section and EFT operators.

Contribution

It introduces a novel neural network-based analysis to search for same-charge top-quark pairs and constrains EFT operator coefficients with the ATLAS data.

Findings

No significant excess observed over the Standard Model prediction.

Upper limit on the production cross-section of 1.6 fb at 95% CL.

Constraints placed on Wilson coefficients of specific EFT operators.

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.