Measurement of the energy asymmetry in $t\bar{t}j$ production at 13 TeV with the ATLAS experiment and interpretation in the SMEFT framework

TL;DR

This paper measures the energy asymmetry in top-quark pair production with an associated jet at 13 TeV using ATLAS data, finds agreement with the Standard Model, and explores its sensitivity to SMEFT operators.

Contribution

It provides the first measurement of the energy asymmetry in $tar{t}j$ production at 13 TeV and interprets the results within the SMEFT framework, highlighting its potential in global fits.

Findings

Energy asymmetry measured to be -0.043±0.020 in the largest asymmetry bin.

Results agree with the Standard Model predictions at NLO accuracy.

Demonstrates the sensitivity of the energy asymmetry to top-quark chirality in SMEFT.

Abstract

A measurement of the energy asymmetry in jet-associated top-quark pair production is presented using 139 $\mathrm{fb}^{-1}$ of data collected by the ATLAS detector at the Large Hadron Collider during $pp$ collisions at $\sqrt{s}=13$ TeV. The observable measures the different probability of top and antitop quarks to have the higher energy as a function of the jet scattering angle with respect to the beam axis. The energy asymmetry is measured in the semileptonic $t\bar{t}$ decay channel, and the hadronically decaying top quark must have transverse momentum above $350$ GeV. The results are corrected for detector effects to particle level in three bins of the scattering angle of the associated jet. The measurement agrees with the SM prediction at next-to-leading-order accuracy in quantum chromodynamics in all three bins. In the bin with the largest expected asymmetry, where the jet is emitted perpendicular to the beam, the energy asymmetry is measured to be $-0.043\pm0.020$, in agreement with the SM prediction of $-0.037\pm0.003$. Interpreting this result in the framework of the Standard Model effective field theory (SMEFT), it is shown that the energy asymmetry is sensitive to the top-quark chirality in four-quark operators and is therefore a valuable new observable in global SMEFT fits.