ar X iv : h ep - e x / 05 01 06 5 v 1 2 5 Ja n 20 05 Electromagnetic and Weak Moments of the τ - Lepton ∗

In the Standard Model (SM) [1] leptons are pointlike fermions. The magnetic moments are predicted with high precision by the theory and the electric dipole moments must be zero. The moments of the electron are measured with high precision [2] and found in perfect agreement with the predictions. For the muon magnetic moment a discrepancy of 2.7 standard deviations is found between recent measurements and the prediction [3], giving rise to think about a possible indication of physics beyond the SM. A deviation of the magnetic moments from the predictions of the theory would be a signal for a substructure or new interactions. Furthermore, a measurement of non-zero values of the electric (electromagnetic or weak) dipole moments reveals CP violation. For the τ -lepton, about 17 times heavier than the muon, only rough limits on the moments were derived before the LEP era [4]. At LEP experiments, measurements of the electromagnetic moments are done using the processes ee → ττγ and, recently, ee → eeττ. Also BELLE published a measurement of the electric dipole moment of the τ -lepton in ee → ττ. Weak moments are measured from the process ee → ττat centre-of-mass energies near the Z resonance by several experiments. The ALEPH experiment published a new result using the full data statistics. A review of the experimental results is given.