The 2025 International Workshop on the High Energy Circular Electron Positron Collider

We evaluate the experimental sensitivity to the $CP$-odd admixture in the standard Higgs boson in the process $e^+e^- \to HZ$, which is expected at future lepton collider CEPC with $\sqrt{s}=240~\text{GeV}$ and statistics of $5.6~\text{ab}^{-1}$. Using the Whizard generator with Higgs Characterisation model and DELPHES detector simulation framework we obtain data samples with different $CP$-odd Higgs admixture parameters $\tilde{c}_{ZZ}$. The initial state radiation (ISR) effects are taken into account in Whizard. Angular and ISR energy shift distributions are used to distinguish the $CP$-odd and $CP$-even Higgs components. Upper limits on the $CP$-odd Higgs admixture parameter are obtained.