Search for the Electric Dipole Moment of the tau Lepton

TL;DR

This study searches for a CP violation signal in the tau lepton's electric dipole moment using data from the Belle detector, setting new upper limits on its real and imaginary components.

Contribution

First measurement of the tau lepton's electric dipole moment using optimal observable analysis with Belle data at KEKB.

Findings

No significant CP violation detected 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 CP violation signature arising from an electric dipole moment (d_tau) of the tau lepton in the e+e- -> tau+tau- reaction. Using an optimal observable method and 29.5 fb^{-1} of data collected with the Belle detector at the KEKB collider at sqrt{s} = 10.58 GeV, we find Re(d_tau) = (1.15 +- 1.70) x 10^{-17} ecm and Im(d_tau) = (-0.83 +- 0.86) x 10^{-17} ecm 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).