Electric dipole moment of the top quark and CP-violating asymmetries in γγ→tt̅

Abstract

CP violation can arise in the production of top-quark–top-antiquark pair in photon-photon collisions in the presence of a nonzero electric dipole coupling of the top quark. This can show up in the distribution of leptons produced in the subsequent decay of the quarks. We study CP-violating asymmetries in the final-state leptons under the assumption that CP violation occurs in the production of the top-quark pair, neglecting CP violation in the decay. The asymmetries defined can be used to determine the imaginary part of the electric dipole form factors. A γγ collider with photon beams generated from laser backscattering off electron beams with an integrated geometric luminosity of 20fb⁻¹ can put a limit of the order of 10⁻¹⁷ecm on the imaginary part of the electric dipole form factor of the top quark if the electron beams have longitudinal polarization and the laser beams have circular polarization.