Decay-lepton angular distribution in polarized $e^+e^- o t$ and $CP$-violating dipole couplings of the top quark

摘要

In the presence of an electric dipole coupling of $t \bar t$ to a photon, andan analogous ``weak" dipole coupling to the $Z$, $CP$ violation in the process$e^+e^- \rightarrow t \bar t$ leads to the polarization of the top andanti-top. This polarization can be analyzed by studying the energy and angulardistributions of a decay charged lepton (anti-lepton) when the top (anti-top)decays leptonically. We have obtained analytic expressions for thesedistributions when either $t$ or $\overline t$ decays leptonically. We studytwo types of simple $CP$-violating angular asymmetries which do not need tofsimple $CP$-violating angular asymmetries which do not need the fullreconstruction of the $t$ or $\bar t$. These together can help to determine theelectric and weak dipole form factors independently. We have also shown how theuse of longitudinal beam polarization can help to do this with only oneasymmetry measurement, and to imprhelp to do this with only one asymmetrymeasurement, and to improve the sensitivity.