CP-violating Zγγ and top-quark electric dipole couplings in γγ→tt̅

Abstract

An effective anomalous CP-violating Zγγ coupling can give rise to observable CP-odd effects in γγ→tt̅. We study certain asymmetries in the decay lepton distributions in γγ→tt̅ arising from top decay in the presence of a CP-violating Zγγ coupling as well as a top-quark electric dipole coupling. We find that a photon linear collider with geometric luminosity of 20 fb⁻¹ can put limits of the order of 0.1 on the imaginary part of the CP-violating anomalous Zγγ coupling using these asymmetries.