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.
For models in which the constituents interact with vector couplings of strength g /4+-1, the energy scale A~for the contact interaction is measured to be greater than 1419. 0 GeV at the 95%%uo confidence level. %'e set limits on the production of supersymmetric scalar electrons through s-channel single-photon annihilation and t-channel inelastic scattering. Using events with two noncollinear electrons and no other charged or observed neutral particles in the final state, we see one event which is consistent with a simple supersymmetric model but which is also consistent with QED. This allows us to exclude the scalar electron to 95% confidence level in the mass range 1.8 to 14.2 GeV/c .
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