Probing the indefinite CP nature of the Higgs Boson through decay distributions in the process $e^+e^-\to t\bar{t}\Phi$

TL;DR

This study investigates the potential to determine the CP nature of the Higgs boson at the ILC by analyzing decay distributions in the process e+e- → t t̄ Φ, highlighting the sensitivity to CP-odd components and the role of beam polarization.

Contribution

It compares minimal and realistic models for CP violation in the Higgs sector, demonstrating the effectiveness of decay distributions and beam polarization in probing CP properties.

Findings

Decay distributions are sensitive to CP-odd components in the Two-Higgs Doublet Model.

Beam polarization enhances the ability to detect CP-violation effects.

Small CP-odd admixtures can be distinguished with high precision at the ILC.

Abstract

The recently discovered scalar resonance at the LHC is now almost confirmed to be a Higgs Boson, whose CP properties are yet to be established. At the ILC with and without polarized beams, it may be possible to probe these properties at high precision. In this work, we study the possibility of probing departures from the pure CP-even case, by using the decay distributions in the process $e^+ e^- \to t \bar{t} \Phi$, with $\Phi$ mainly decaying into a $b\bar b$ pair. We have compared the case of a minimal extension of the SM case (Model I) with an additional pseudoscalar degree of freedom, with a more realistic case namely the CP-violating Two-Higgs Doublet Model (Model II) that permits a more general description of the couplings. We have considered the ILC with $\sqrt{s}=800$\,GeV and integrated luminosity of $300\, {\rm fb}^{-1}$. Our main findings are that even in the case of small departures from the CP-even case, the decay distributions are sensitive to the presence of a CP-odd component in Model II, while it is difficult to probe these departures in Model I unless the pseudoscalar component is very large. Noting that the proposed degrees of beam polarization increases the statistics, the process demonstrates the effective role of beam polarization in studies beyond the Standard Model. Further, our study shows that an indefinite CP Higgs would be a sensitive laboratory to physics beyond the SM.