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, awτ, and of the weak electric dipole moment, dwτ, of the τ lepton is performed. These quantities are obtained from angular distributions in <math><mtext>e</mtext><msup><mi></mi><mn>+</mn></msup><mtext>e</mtext><msup><mi></mi><mn>−</mn></msup><mtext>→τ</mtext><msup><mi></mi><mn>+</mn></msup><mtext>τ</mtext><msup><mi></mi><mn>−</mn></msup><mtext>→h</mtext><msup><mi></mi><mn>+</mn></msup><mtext>ν</mtext><mtext>̄</mtext><msub><mi></mi><mn>τ</mn></msub><mtext>h</mtext><msup><mi></mi><mn>−</mn></msup><mtext>ν</mtext><msub><mi></mi><mn>τ</mn></msub></math>, where h is a π or a p. The results are: Re(awτ)=(0.0±1.6±2.3)×10−3, Im(awτ)=(−1.0±3.6±4.3)×10−3 and Re(dwτ)=(−0.44±0.88±1.33)×10−17e·cm. This is the first direct measurement of awτ.