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

Abstract

The QED processes e⁺e^-→e⁺e^-μ⁺μ^- and e⁺e^-→e⁺e^-Τ⁺Τ^- are studied with the L3 detector at LEP using an untagged data sample collected at centre-of-mass energies 161 GeV≤√ s≤ 209 GeV. The Τ-pairs are observed through the associated decay of one Τ into eνν and the other into π πν. The cross sections are measured as a function of √s. For muon pairs, the cross section of the γγ→ μ⁺μ^- process is also measured as a function of the two-photon centre-of-mass energy for 3 GeV?W_γγ?40 GeV. Good agreement is found between these measurements and the β(α⁴) QED expectations. In addition, limits on the anomalous magnetic and electric dipole moments of the Τlepton are extracted.