The $e^+ e^- \rightarrow Z H$ Process in the SMEFT Beyond Leading Order

TL;DR

This paper analyzes the impact of dimension-6 SMEFT operators on the $e^+ e^- ightarrow Z H$ process at NLO, highlighting sensitivities to new physics effects beyond leading order in future collider experiments.

Contribution

It provides a comprehensive NLO analysis of SMEFT effects in $e^+ e^- ightarrow Z H$, including operators not visible at tree level, and compares collider sensitivities with other experimental constraints.

Findings

NLO corrections significantly alter predictions for certain operators.

Future colliders can probe operators beyond current LHC and EDM limits.

Sensitivity to Higgs and top-quark related operators is enhanced at NLO.

Abstract

We systematically study potential effects of Beyond the Standard Model physics in the $e^+ e^- \rightarrow Z H$ process. To this end, we include all relevant dimension-6 Standard Model Effective Field Theory operators and work to next-to-leading order (NLO) accuracy in the electroweak coupling. We consider both polarized and unpolarized electron and positron beams and present results for $\sqrt{s}=240, ~365$ and $500~{\rm GeV}$, emphasizing contributions where the NLO predictions differ significantly from the leading order results. At NLO, a sensitivity arises to operators that do not contribute at tree level, such as the Higgs tri-linear coupling, CP-violating operators, and dimension-6 operators involving the top quark, among many others. We compare the prospects of future $e^+e^-$ colliders to explore these new physics effects with existing measurements from the LHC, electron EDMs (for CP violating operators), and Z pole measurements.