Determination of CP-violating Higgs couplings with transversely-polarized beams at the ILC

We study possible CP-violation effects of the Higgs to $Z$-boson coupling at a future $e^{+}{e}^{-}$ collider, e.g. the International Linear Collider (ILC). We find that the azimuthal angular distribution of the muon pair, produced by $e^{+}{e}^{-}\to HZ\to H{\mu }^{+}{\mu }^{-}$, can be sensitive to such a CP-violation effect when we apply initial transversely polarized beams. Based on this angular distribution, we construct a CP sensitive asymmetry and obtain this asymmetry by $\mathtt{\text{Whizard}}$ simulation. By comparing the SM prediction with 2$\sigma$ range of this asymmetry, we estimate the discovery limit of the CP-odd coupling in $HZZ$ interaction.