Polarized $Z$ cross sections in Higgsstrahlung for the determination of anomalous $ZZH$ couplings

TL;DR

This paper proposes using polarized Z boson cross sections in Higgsstrahlung at electron-positron colliders to more precisely measure and isolate anomalous $ZZH$ couplings, enhancing understanding of Higgs interactions.

Contribution

It introduces specific polarized Z cross section combinations that help isolate different $ZZH$ couplings, applicable across various theoretical models, with insights on the longitudinal Z fraction's robustness.

Findings

Certain polarized cross sections isolate specific $ZZH$ couplings.

Longitudinal Z fraction remains insensitive to anomalous couplings.

Proposed measurements can effectively probe anomalous $ZZH$ interactions.

Abstract

The production of a Higgs boson in association with a $Z$ at an electron-positron collider is one of the cleanest methods for the measurement of the couplings of the Higgs boson. In view of the large production cross section at energies a little above the threshold, it seems feasible to make a more detailed study of the process by measuring the cross sections for polarized $Z$ in order to measure possible anomalous $ZZH$ couplings. We show that certain combinations of cross sections in $e^+e^- \to ZH$ with different $Z$ polarizations help to enhance or isolate the effect of one of the two kinds of $ZZH$ couplings possible on general grounds of CP and Lorentz invariance. These combinations can be useful to get information on the $ZZH$ coupling in the specific contexts of an effective field theory, two-Higgs-doublet models, and composite Higgs models, in a relatively model-independent fashion. We find in particular that the longitudinal helicity fraction of the $Z$ is expected to be insensitive to anomalous couplings, and would be close to its value in the standard model in the scenarios we consider. We also discuss the sensitivity of the proposed measurements to the anomalous couplings.