Single decay-lepton angular distributions in polarized e~+e~-→tt and simple angular asymmetries as a measure of CP-violating top dipole couplings

摘要

In the presence of an electric dipole coupling of tt to a photon, and an analogous 'weak' dipole coupling to the Z, CP violation in the process e~+e~-→tt results in modified polarization of the top and the anti-top. This polarization can be analyzed by studying the angular distributions of decay charged leptons when the top or anti-top decays leptonically. Analytic expressions are presented for these distributions when either t or t decays leptonically, including O(α_s) QCD corrections in the soft-gluon approximation. The angular distributions are insensitive to anomalous interactions in top decay. Two types of simple CP-violating polar-angle asymmetries and two azimuthal asymmetries, which do not need the full reconstruction of the t or t, are studied. Independent 90% CL limits that may be obtained on the real and imaginary parts of the electric and weak dipole couplings at a linear collider operating at s~(1/2) = 500 GeV with integrated luminosity 500 fb~(-1) and also at s~(1/2) = 1000 GeV with integrated luminosity 1000 fb~(-1) have been evaluated. The effect of longitudinal electron and/or positron beam polarizations has been included.