Wide-Angle Bremsstrahlung

Abstract

We have extended our earlier measurements of the cross section for wide-angle electron bremsstrahlung. Besides the data for symmetric final electron and photon angles already published, we report results for asymmetric angles. The circulating electron beam of the Cornell 10-GeV synchrotron struck a carbon target and was monitored by observing the forward bremsstrahlung beam. Wide-angle photons were counted in coincidence with the corresponding scattered electrons. The recoil momentum of the unobserved nucleus was minimized. The experimental cross sections are compared with the predictions of the Bethe-Heitler formula corrected for elastic and inelastic nuclear form factors and for virtual nuclear Compton scattering. The agreement is excellent, confirming the predictions of quantum electrodynamics for timelike electron four-momenta up to 1.2 GeV. If one assumes a deviation in the experiment/theory ratio proportional to the square of the final electron-photon invariant mass, the 95% confidence upper limit on the corresponding distance parameter is ${{\ensuremath{\Lambda}}_{(2)}}^{\ensuremath{-}1}=5.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ cm. The upper limit for a fourth-power deviation is ${{\ensuremath{\Lambda}}_{(4)}}^{\ensuremath{-}1}=6.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ cm.