Probing Top Quark-Electron Interactions at Future Colliders

Abstract

Top quark interactions offer a window into possible new high scale physics and many models of new physics predict that the top quark interactions will deviate significantly from those predicted by the Standard Model (SM). We present an analysis of the experimental restrictions on anomalous 4-fermion $e^+e^- t {\overline{t}}$ operators that is accurate to next-to-leading order (NLO) in both the electroweak and QCD interactions within the Standard Model Effective Field Theory framework. At NLO, there is sensitivity to an extended set of anomalous interactions beyond those probed at leading order. A comparison of current limits from electroweak precision observables, along with expected future limits from Drell-Yan and $t{\overline{t}}e^+e^-$ production at the high luminosity LHC, from deep inelastic scattering at the EIC, and from projected sensitivities at the future FCC-ee and CEPC machines demonstrates that each of these programs extends the precision understanding of the interactions of top quarks.

Figures (5)

• Figure 1: Representative Feynman diagrams for the Drell-Yan process $q\bar{q}\to e^-e^+$ (left), associated Z boson-Higgs production (middle), and top-pair production (right).
• Figure 1: Same as Fig. \ref{['fig:bound']} in the main text, except the Wilson coefficients are set to $4\pi$.
• Figure 2: The partonic Drell-Yan cross section as a function of $\sqrt{{\hat{s}}} = m_{\ell\ell}$, comparing the SM prediction (black) with the contribution from the operator $\mathcal{O}^{(3),1133}_{\ell q}$ (solid red). The contribution from $\mathcal{O}^{(3),1133}_{\ell q}$ is separated into logarithmic (dashed red) and non-logarithmic (dotted red) terms.
• Figure 3: The $2\sigma$ limits on $C^{3311}_{qe}$-$C^{1133}_{eu}$ (upper panel) and $C^{(3),1133}_{\ell q}$-$C^{(1),1133}_{\ell q}$ (lower panel) at current and future colliders. In the upper panel, the FCC-ee (365 GeV) projection appears as a dot at the origin (0,0). For clarity, we mark it with a blue star. All other operators are set to $0$ and $\Lambda=1$ TeV. The calculation does not include contributions of $\mathcal{O}(1/\Lambda^4)$.
• Figure 4: The 2$\sigma$ marginalized bounds on the scale $\Lambda$ from a global fit to the $4$-fermion operators considered in this work. The Wilson coefficients are set to 1. All contributions of $\mathcal{O}(1/\Lambda^4)$ are dropped. For the HL-LHC, we consider only including the tree-level process $pp\rightarrow t \bar{t} e^- e^+$ (cyan) and including both the tree-level and NLO Drell-Yan processes (light cyan). The FCC-ee projections consist of three components, corresponding to FCC-ee $Z$-pole, FCC-ee at $WW$ threshold, and FCC-ee at $\sqrt{s}=365~\textrm{ GeV}$, shown in increasingly lighter shades of red. The contribution from FCC-ee at the $WW$ threshold is indistinguishable from the $Z$-pole contribution for operators $\mathcal{O}^{(3)}_{\ell q}$, $\mathcal{O}_{qe}$, and $\mathcal{O}_{eu}$. Higgstrahlung does not make an observable contribution to the FCC-ee bands.