Search for the Electric Dipole Moment of the tau lepton

TL;DR

This paper reports a search for the electric dipole moment of the tau lepton using e+e- collision data, setting new limits on its real and imaginary components to test CP violation.

Contribution

First measurement of the tau lepton's electric dipole form factor using optimal observable analysis with Belle data.

Findings

No significant CP violation observed in tau EDM.

Set the most stringent limits to date on Re(d_tau) and Im(d_tau).

Results consistent with Standard Model predictions.

Abstract

We have searched for a T/CP violation signature arising from an electric dipole form factor (d_tau) of the tau lepton in the e+e- -> tau+tau- reaction. Using an optimal observable method for 29.5 fb^{-1} of data collected with the Belle detector at the KEKB collider at sqrt{s}=10.58 GeV, we obtained the preliminary result Re(d_tau) = (1.15 +- 1.70) x 10^{-17} ecm and Im(d_tau) = (-0.83 +- 0.86) x 10^{-17} ecm for the real and imaginary parts of d_tau, respectively, and set the 95% confidence level limits -2.2 < Re(d_tau) < 4.5 (10^{-17} ecm) and -2.5 < Im(d_tau) < 0.8 (10^{-17} ecm).