Precision test of QED by direct comparison of e+e− → γγ and e+e− → e+e− at 29 GeV

Abstract The ratio of differential cross sections for the reactions e + e − → γγ and e + e − → e + e − is measured at s = 29 GeV in the central polar angle region, |cos θ | α 3 . The ratio of these ratios, integrated over this angular region, is 1.007±0.009±0.008, demonstrating excellent agreement between theory and experiment. The 95% confidence limits on the QED cut-off parameters for the γγ final state are Λ + > 59 GeV and Λ - > 59 GeV.