Probing top quark neutral couplings in the Standard Model Effective Field Theory at NLO QCD

TL;DR

This paper provides NLO QCD predictions for top quark neutral couplings in the Standard Model Effective Field Theory, including total and differential cross sections, to aid experimental analysis and interpretation.

Contribution

It offers the first comprehensive NLO QCD predictions for top quark neutral couplings in SMEFT, including full CP-even dimension-six operators and event generation capabilities.

Findings

NLO QCD corrections significantly affect cross sections and distributions.

Uncertainties from higher-order corrections are quantified.

Framework enables precise interpretation of top quark measurements.

Abstract

Top quark pair production in association with a $Z$-boson or a photon at the LHC directly probes neutral top-quark couplings. We present predictions for these two processes in the Standard Model (SM) Effective Field Theory (EFT) at next-to-leading (NLO) order in QCD. We include the full set of CP-even dimension-six operators that enter the top-quark interactions with the SM gauge bosons. For comparison, we also present predictions in the SMEFT for top loop-induced $HZ$ production at the LHC and for $t\bar{t}$ production at the ILC at NLO in QCD. Results for total cross sections and differential distributions are obtained and uncertainties coming from missing higher orders in the strong coupling and in the EFT expansions are discussed. NLO results matched to the parton shower are available, allowing for event generation to be directly employed in an experimental analyses. Our framework provides a solid basis for the interpretation of current and future measurements in the SMEFT, with improved accuracy and precision.