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

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