Tests of QED at LEP energies using e+e- → γγ(γ) and e+e- → ℓ+ℓ-γγ

Abstract Total and differential cross sections for the process e + e − → γγ ( γ ), and the total cross section for the process e + e − → γγγ , are measured at energies around 91 GeV using the data collected with the L3 detector from 1991 to 1993. We set lower limits, at 95% CL, on a contact interaction energy scale parameter Λ > 602 GeV, on the mass of an excited electron m e ∗ >146 GeV and on the QED cut-off parameters Λ + > 149 GeV and Λ _ > 143 GeV. Upper limits are also set o branching fractions of Z decaying into γγ , π ° and ηγ of 5.2 × 10 −5 , 5.2 × 10 −5 and 7.6 × 10 −5 respectively. The reactions e + e − → l + l − nγ (l = e , μ , τ ) are studied using the data collected from 1990 to 1994. The data are consistent with the QED expectations.