The $q^2$ running of effective QED coupling $\alpha \left(q^2\right)$ is measured in a spacelike region, $\left(10\mathrm{GeV}{)}^2\le {-q}^2\le \right(54\mathrm{GeV}{)}^2$, using Bhabha-scattering and muon-pair production data at $e^{+}{e}^{-}$ 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 $\alpha \left(q^2\right)/\alpha \left(t_0\right)$ with $t_0=-(10\mathrm{GeV}{)}^2$.

• Received 9 June 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.2428