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 ππν. 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

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