Measurement of the weak dipole moments of the τ lepton

Abstract

Using the data collected by the L3 experiment at LEP from 1991 to 1995 at energies around the Z mass, a measurement of the weak anomalous magnetic dipole moment, a^w_τ, and of the weak electric dipole moment, d^w_τ, of theτ lepton is performed. These quantities are obtained from angular distributions in e⁺e⁻ → τ⁺τ⁻ → h⁺ν̅_τh⁻ν_τ , where h is a π or a ρ. The results are: Re()=(0.0±1.6±2.3)x10⁻³, Im(a^w_τ)=(−1.0±3.6±4.3)×10⁻³ and Re(d^w_τ)=(−0.44±0.88±1.33)×10⁻¹⁷ e.cm. This is the first direct measurement of a^w_τ.