Muon-pair and tau-pair production in two-photon collisions at LEP

The QED processes e(+)e(-) --\u3e e(+)e(-)mu(+)mu(-) and e(+)e(-) --\u3e e(+)e(-)tau(+)tau(-) are studied with the L3 detector at LEP using an untagged data sample collected at centre-of-mass energies 161 GeV less than or equal to roots less than or equal to 209 GeV, The tau-pairs are observed through the associated decay of one tau into evv and the other into pipiv. The cross sections are measured as a function of roots. For muon pairs, the cross section of the gammagamma --\u3e mu(+)mu(-) process is also measured as a function of the two-photon centre-of-mass energy for 3 GeV less than or equal to Wgammagamma less than or equal to 40 GeV Good agreement is found between these measurements and the O(alpha(4)) QED expectations. In addition, limits on the anomalous magnetic and electric dipole moments of the T lepton are extracted. (C) 2004 Published by Elsevier B.V