Title: Probing the CP properties of top Yukawa coupling at an e+e− collider

 Abstract:

We study consequences of CP violation in the htt ̄Yukawa coupling through the process e+e− →h(125)tt. The helicity amplitudes are calculated in the tt rest frame, where the initial e e current and the final Higgs boson have the same three-momentum. CP-violating asymmetries appear not only in the azimuthal angle between the e+e− plane and the tt ̄ plane about the Higgs momentum direction, but also in the correlated decay angular distributions of t and tbar. Complete description of the production and decay angular distributions are obtained analytically, including both leptonic and hadronic decays of t and tbar. We study the ultimate sensitivity to the CP-violating htt coupling at a few center-of-mass energies. Our analysis shows that the possibility of discovering CP-violating htt ̄ coupling improves significantly by studying tt ̄ decay angular correlations, and more importantly, by increasing its energy upgrade target from s = 500 GeV to 550 GeV.