Measurement of the Running of Effective QED Coupling at Large Momentum Transfer in the Spacelike Region

Abstract

The ${q}^{2}$ running of effective QED coupling $\ensuremath{\alpha}({q}^{2})$ is measured in a spacelike region, $(10\mathrm{GeV}{)}^{2}\ensuremath{\le}{\ensuremath{-}q}^{2}\ensuremath{\le}(54\mathrm{GeV}{)}^{2}$, using Bhabha-scattering and muon-pair production data at ${e}^{+}{e}^{\ensuremath{-}}$ collisions with a center-of-mass energy of 57.77 GeV. The result verifies the prediction of a theoretical estimation with a precision of better than 1% in terms of $\ensuremath{\alpha}({q}^{2})/\ensuremath{\alpha}({t}_{0})$ with ${t}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}(10\mathrm{GeV}{)}^{2}$.