# Probing anomalous gauge-Higgs couplings using $Z$ boson polarization at $e^+ e^-$ colliders

## TL;DR

This paper investigates how the polarization of the Z boson in the Higgsstrahlung process at future electron-positron colliders can be used to detect and constrain anomalous gauge-Higgs couplings, providing a new method to probe physics beyond the Standard Model.

## Contribution

It introduces a novel approach using Z boson polarization and angular asymmetries to constrain anomalous $ZZH$ couplings at future colliders.

## Key findings

- Potential to significantly constrain anomalous couplings at 250 GeV and 500 GeV.
- Angular asymmetries effectively relate to Z polarization observables.
- Method applicable with various beam polarization configurations.

## Abstract

We study possible new physics interactions in the $ZZH$ vertex contributing to the Higgsstrahlung process $e^+ e^- \to ZH$ at proposed future $e^+e^-$ colliders using the polarization of the $Z$ as a probe. We calculate the spin density matrix of the $Z$ for the process and determine the eight independent polarization parameters of the $Z$ boson which have the potential to constrain the anomalous couplings. We study angular asymmetries using the decay leptons from the $Z$ boson which are simply related to the polarization observables. We also estimate the limits that can be placed on the anomalous couplings using measurements of these angular asymmetries at centre of mass energies of 250 GeV and 500 GeV and various combinations of polarized $e^+$ and $e^-$ beams.