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

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.

Figures (13)

• Figure 1: The Feynman diagrams for the partonic process contributing to $p p \to t \overline t$ at leading order within the SM: gluon fusion (top) and pair annihilation (bottom).
• Figure 2: The same as Fig. \ref{['fig:lo_diagrams_sm']} but within the SMEFT. The blobs denote SMEFT operator insertions.
• Figure 3: The relevant SMEFT Feynman rules for the partonic process of interest, adopted from Degrande:2020evl.
• Figure 4: The top-quark single-differential $p_T$ distribution in $t\overline t$ production within the SM across the bins at LO (left), NLO (center), and NNLO (right) at 13 TeV (top) and 13.6 TeV (bottom).
• Figure 5: The same as Fig. \ref{['fig:pt_distr']} but for the top-quark single-differential $y$ distribution.