Single decay-lepton angular distributions in polarized e+e- --> t tbar
and simple angular asymmetries as a measure of CP-violating top dipole
couplings
In the presence of an electric dipole coupling of t-tbar to a photon, and an
analogous "weak" dipole coupling to the Z, CP violation in the process e+e- -->
t tbar results in modified polarization of the top and 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 tbar decays
leptonically, including O(alpha_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 tbar, 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 sqrt{s}=500 GeV with integrated
luminosity 500 fb^{-1} and also at sqrt{s}=1000 GeV with integrated luminosity
1000 fb^{-1} have been evaluated. The effect of longitudinal electron and/or
positron beam polarizations has been included.Comment: 26 pages, latex, figures included as latex files, version appearing
in Pramana - Journal of Physics, minor corrections and note added in proo