The cross section of the process $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ was measured in the spherical neutral detector experiment at the VEPP-2M $e^{+}{e}^{-}$ collider in the energy region $\sqrt{s}=980$, 1040–1380 MeV. The event numbers of the process $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ were normalized to the integrated luminosity measured using $e^{+}{e}^{-}\to e^{+}{e}^{-}$ and $e^{+}{e}^{-}\to \gamma \gamma$ processes. The ratio of the measured cross section to the theoretically predicted value is $1.006\pm 0.007\pm 0.016$ and $1.005\pm 0.007\pm 0.018$ in the first and second case, respectively. Using results of the measurements, the electromagnetic running coupling constant $\alpha$ in the energy region $\sqrt{s}=1040–1380\mathrm{MeV}$ was obtained $⟨1/\alpha ⟩=134.1\pm 0.5\pm 1.2$ and this is in agreement with theoretical expectation.

• Received 5 October 2008

DOI:https://doi.org/10.1103/PhysRevD.79.112012