Precise measurement of CP violating τ EDM through e+e- → γ*, ψ(2s) → τ+τ-

A nonzero electric dipole moment of a tauon, d tau, signals CP violation and provides an important probe for new physics. We study methods to measure d tau at low energy e+e- colliders through the processes e+e- -> gamma*, psi(2S) -> tau+tau- with tau +/- decays into a charged hadron and a tau neutrino. We point out that, with measuring energies of the charged hadron, Im(d tau) can be measured. On the other hand, selecting events of tau decays after traveling more than the detector resolution distance, Re(d tau) can also be determined. We find that the precision at Super Tau-Charm Facility (STCF) running at the center energy of m psi(2S) for 10 year data accumulation, the precision of Im(d tau) and Re(d tau) are found to be 1.8 and 11 in unit of 10-18e cm, respectively. The sensitivity for d tau measurement precision at the STCF can be reached its optimum at a central energy of 6.3 GeV, achieving a precision of 0.7 for Im(d tau) and 2.8 for Re(d tau) in unit of 10-18e cm.