Experimental study of the reactions e+e:e+e and e+e = yy at 29 GeV

This paper reports measurements of the differential cross sections for the reactions e+e — +e+e {Bhabha scattering) and e e ~yy {y-pair production). The reactions are studied at a center-ofmass energy of 29 GCV aud in the polar-angular region I cos8 I & 0.55. A direct cross-section comparison between these two reactions provides a sensitive test of the predictions of quantum electrodynamics (QED) to order n . When the ratio of y-pair to Bhabha experimental cross sections, integrated over I cose I &0.55, is divided by the same ratio predicted from n QED theory, the result is 1.007+0.009%0.008. The 95%-confidence limits on the QED-cutoff parameters are A+ y 154 GeV and A ~ 220 GeV for Bhabha scattering, and A+ g 59 GeV and A ~ 59 GeV for y-pair production.