Search for anomalous weak dipole moments of the tau lepton

TL;DR

This paper reports measurements of the tau lepton's anomalous weak dipole moments using data from ALEPH, setting bounds on their real and imaginary components and finding no evidence of physics beyond the Standard Model.

Contribution

First simultaneous measurement of both the real and imaginary parts of the tau's anomalous weak magnetic and electric dipole moments using semileptonic decay data.

Findings

No evidence of new physics detected.

Set 95% CL bounds on dipole moments.

Measured bounds: |Re, mu_tau| < 1.14e-3, |Im, mu_tau| < 2.65e-3, |Re, d_tau| < 0.91e-3, |Im, d_tau| < 2.01e-3.

Abstract

The anomalous weak dipole moments of the tau lepton are measured in a data sample collected by ALEPHfrom 1990 to 1995 corresponding to an integrated luminosity of 155pb-1. Tau leptons produced in the reaction e+e- -> tau+tau- at energies close to the Z mass are studied using their semileptonic decays to pi, rho, a_1 -> pi 2pi0 or a_1 -> 3 pi. The real and imaginary components of both the anomalous weak magnetic dipole moment and the CP-violating anomalous weak electric dipole moment, Re,mu_tau, Im,mu_tau, Re, d_tau and Im, d_tau, are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained 95% CL: |Re, mu_tau | < 1.14 x 10-3, |Im}, mu_tau | < 2.65 x 10-3, |Re}, d_tau | < 0.91 x 10-3, and |Im, d_tau | < 2.01 x 10-3.