Photoproduction of Wide-Angle Electron-Positron Pairs at High Energies

Abstract

Using the DESY 6.2-GeV electron synchrotron, we have measured the photoproduction on carbon of electron-positron pairs, for a range in the invariant pair mass of 150-550 MeV. To detect the pairs and to discriminate against the intense pion background, a magnetic spectrometer, counters, and fast electronics were used. The results are in agreement with the predictions of first-order quantum electrodynamics, in contradiction with earlier experiments. A comparison of our results with other tests of quantum electrodynamics at small distances is discussed.