A Search for the Electric Dipole Moment of the Tau-Lepton

TL;DR

This paper reports the first direct search for the electric dipole moment of the tau lepton using the ARGUS detector, finding no evidence of CP violation and setting upper limits on the formfactor.

Contribution

It introduces a novel direct measurement method for the tau lepton's electric dipole formfactor using optimized observables at high energy.

Findings

No evidence of CP violation was observed.

Measured Re(d_tau) and Im(d_tau) are consistent with zero within errors.

Established upper limits on the electric dipole formfactor.

Abstract

Using the ARGUS detector at the e+e- storage ring DORIS II, we have searched for the real and imaginary part of the electric dipole formfactor d_tau of the tau lepton in the production of tau pairs at q^2=100 GeV^2. This is the first direct measurement of this CP violating formfactor. We applied the method of optimised observables which takes into account all available information on the observed tau decay products. No evidence for CP violation was found, and we derive the following results: Re(d_tau)=(1.6+-.9)*10^(-16) ecm and Im(d_tau)=(-0.2+-0.8)*10^(-16) ecm, where statistical and systematic errors have been combined.