CP violation and electric-dipole-moment at low energy $τ$ production with polarized electrons

Abstract

The new proposals for high luminosity B/Flavor factories, near and on top of the $Υ$ resonances, allow for a detailed investigation of CP-violation in the $τ$-pair production. In particular, bounds on the tau electric dipole moment can be obtained from genuine CP-odd observables related to the $τ$-pair production. We perform an independent analysis from low energy (10 GeV) data by means of linear spin observables. We show that, for a longitudinally polarized electron beam, a CP-odd asymmetry, associated to the normal polarization term, can be measured at these low energy facilities both at resonant and non resonant energies. In this way, stringent and independent bounds to the tau electric dipole moment, which are orders of magnitude below other high or low energy bounds, can be obtained.