Running of the QED coupling in small-angle Bhabha scattering at LEP

Abstract

Using the OPAL detector at LEP, the running of the effective QED coupling alpha(t) is measured for space-like momentum transfer, 2 \leq -t \leq 6 GeV^2, from the angular distribution of small-angle Bhabha scattering. This is currently the most significant direct observation of the running of the QED coupling in a single experiment and the first clear evidence of the hadronic contribution to the running in the space-like region. Our result is in good agreement with standard evaluations of alpha(t), based on data in the time-like region.Comment: Talks given at the 19th Rencontres De Physique De La Vallee D'Aoste (27.2-5.3.05), La Thuile, Italy and at the 40th Rencontres De Moriond On Electroweak Interactions And Unified Theories (5.3-12.3.05), La Thuile, Italy. Added 1 figure and related text wrt vers.