Test of QED to fourth order by study of four-lepton final states ine+e−interactions at 29 GeV with the Mark II detector

Abstract

We have tested QED to fourth order in the coupling constant $\alpha$ in the large-$Q^2$ region by studying four-lepton final states in $e^{+}{e}^{-}$ interactions with the Mark II detector at the SLAC storage ring PEP ($\sqrt{s}=29\mathrm{}$ GeV). All four final-state particles were detected at large angles with respect to the beam axis. For an integrated luminosity of 205 ${\mathrm{pb}}^{-1\mathrm{}}$, we observed ten $e^{+}{e}^{-}{e}^{+}{e}^{-}$, ten $e^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$, and one ${\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$ events with opposite-charge pair masses greater than 1 GeV/${\mathit{c}}^2$. These events show good agreement with the complete ${\alpha }^4$ QED calculation.