# Characterizing Higgs portal dark matter models at the ILC

## TL;DR

This paper investigates the potential for discovering and distinguishing Higgs portal dark matter models at the ILC, focusing on signal detection, background analysis, and spin discrimination for different DM types.

## Contribution

It provides a detailed analysis of DM discovery prospects and spin discrimination at the ILC within Higgs portal models, highlighting differences between scalar, fermion, and vector DM.

## Key findings

- Hadronic Z decay channel offers better sensitivity than leptonic.
- Light scalar mediators are more discoverable at small DM-mediator coupling.
- Spin discrimination is promising for scalar vs fermion DM, challenging for vector DM.

## Abstract

We study the Dark Matter (DM) discovery prospect and its spin discrimination in the theoretical framework of gauge invariant and renormalizable Higgs portal DM models at the ILC with $\sqrt{s} = 500$ GeV. In such models, the DM pair is produced in association with a $Z$ boson. In case the singlet scalar DM, the mediator is just the SM Higgs boson, whereas for the fermion or vector DM there is an additional singlet scalar mediator that mixes with the SM Higgs boson, which produces significant observable differences. After careful investigation of the signal and backgrounds both at parton level and at detector level, we find the signal with hadronically decaying $Z$ boson provides a better search sensitivity than the signal with leptonically decaying $Z$ boson. Taking the fermion DM model as a benchmark scenario, when the DM-mediator coupling $g_\chi$ is relatively small, the DM signals are discoverable only for benchmark points with relatively light scalar mediator $H_2$. And the spin discriminating from scalar DM is always promising while it is difficult to discriminate from vector DM. As for $g_\chi$ approaching the perturbative limit, benchmark points with the mediator $H_2$ in the full mass region of interest are discoverable. And the spin discriminating from both the scalar and fermion DM are quite promising.