Probing CPV mixing in the Higgs sector in VBF at 1 TeV ILC

With the current precision of measurements by the ATLAS and CMS experiments, it cannot be excluded that a SM-like Higgs boson is a CP violating mixture of CP-even and CP-odd states. We explore this possibility here, assuming Higgs boson production in ZZ-fusion, at 1 TeV ILC, with unpolarized beams. The full simulation of SM background and fast simulation of the signal is performed, simulating 8 ab⁻¹ of data collected with the ILD detector. We demonstrate that the CP mixing angle ΨCP between scalar and pseudoscalar states can be measured with the statistical uncertainty of 3.8 mrad at 68% CL, corresponding to 1.44 · 10⁻⁵ for the CP parameter fCP, for the pure scalar state. This is the first result on sensitivity of an e⁺e⁻ collider to measure fCP in the Higgs production vertex in vector boson fusion.