| This thesis presents tests of quantum electrodynamics (QED), the theory of the electromagnetic force, at order {dollar}alphasp4{dollar} in the dimensionless coupling. The data were accumulated, using the TOPAZ detector at the TRISTAN {dollar}esp+esp-{dollar} collider, in KEK, Japan's National Laboratory for High Energy Physics. An integrated luminosity of 221.8 pb{dollar}sp{lcub}-1{rcub}{dollar}, taken at an average center of mass energy {dollar}={rcub} 57.77{dollar} GeV, was analyzed. Differential cross sections for the reaction {dollar}esp+esp-to esp+esp-musp+musp-{dollar} are presented and various kinematic distributions are compared with theoretical predictions. Strengthening of the electromagnetic coupling with increasing momentum transfer has been observed, by comparing two photon muon production with single photon muon production. We measure {dollar}alpha(Qsp2)sp{lcub}-1{rcub}{dollar} to change from its known value of about 137.036 at {dollar}Qsp2approx0{dollar} (GeV/c){dollar}sp2{dollar} to 129.24 {dollar}pm{dollar} 2.00 (stat) {dollar}pm{dollar} 0.77 (sys) at Q{dollar}sp2{dollar} = (57.77 GeV/c){dollar}sp2{dollar}. These results agree with QED to a high degree of precision and suggest that the forces of nature have strengths which converge as the momentum transfer rises, thus supporting the idea of unification. |
