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

Data taken with the High Resolution Spectrometer detector at the SLAC storage ring PEP were used to test QED to fourth order in the coupling constant $\alpha$. The experiment studied four-lepton final states produced at high $Q^2$ in $e^{+}{e}^{-}$ interactions at $\sqrt{s}=29\mathrm{}$ GeV. All four final-state particles were detected at large angles with respect to the beam axis. We observed $17 e^{+}{e}^{-}{e}^{+}{e}^{-}$, $24 e^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$, and $1 {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$ events with pair masses greater than 1 GeV/${\mathit{c}}^2$ for an integrated luminosity of 291 ${\mathrm{pb}}^{-1\mathrm{}}$. The complete ${\alpha }^4$ QED calculation agrees reasonably well with the data.