$t\bar t$ production as a probe of dimension-6 SMEFT at higher orders

TL;DR

This paper investigates top-antitop production in proton collisions within SMEFT at dimension 6, emphasizing higher-order QCD effects to improve bounds on top chromomagnetic operators.

Contribution

It combines NNLO SM predictions with approximate NNLO SMEFT interference corrections, demonstrating the importance of higher-order effects for robust bounds.

Findings

Higher-order QCD effects stabilize SMEFT interpretations.

Sensitivity to the top chromomagnetic operator reaches up to 3.9 TeV.

Differential distributions provide precise probes of top interactions.

Abstract

We study top-antitop pair production in proton-proton collisions within the Standard Model Effective Field Theory (SMEFT) at dimension 6. We focus on the top chromomagnetic operator $C_{tG}$ together with the four-quark operators relevant for unpolarized $t{\bar t}$ production. We analyze the top-quark single-differential transverse-momentum ($p_T$) and rapidity ($y$) distributions and the double-differential distributions in $p_T$ and $y$ ($p_T\times y$) at 13~TeV, and we present projections for 13.6~TeV using the same binning. Our highest-order setup combines next-to-next-to-leading-order (NNLO) Standard Model (SM) predictions with approximate NNLO (aNNLO) SM--SMEFT interference corrections. We find that higher-order QCD effects are essential for a stable SMEFT interpretation, yielding substantially more robust bounds and milder parameter degeneracies. The strongest sensitivity is obtained for $C_{tG}$. In the combined highest-order analysis of the 13-TeV results and 13.6-TeV projections, we obtain sensitivity to effective scales up to 3.9~TeV. Our results show that higher-order differential top-pair production provides a precise and theoretically controlled probe of the top chromomagnetic interaction.