CP Violation in top pair production at an e^+e^- collider

Abstract

We investigate possible CP violating effects in $e^+e^-$ annihilation into top quark pairs. One of the interesting observable effects is the difference in production rates between the two CP conjugate polarized states $t_L\bar t_L$ and $t_R\bar t_R$. The result is an asymmetry in the energy spectra of the lepton and the anti-lepton from the heavy quark decays. Another CP-odd observable is the up-down asymmetry of the leptons with respect to the reaction plane. These two asymmetries measure complementarily the absorptive and dispersive form factors of the electric dipole moment. Finally, as an illustration, we calculate the size of the CP violating form factors in a model where the CP nonconservation originates from the Yukawa couplings of a neutral Higgs boson.