POLARIZATION PHENOMENA IN SMALL-ANGLE PHOTOPRODUCTION OF E(-) PAIRS AND THE GERASIMOV-DRELL-HEARN SUM-RULE()E()

Photoproduction of e(+)e(-) pairs at small angles is investigated as a tool to determine the functions f(1) and f(2) entering the real-photo n forward Compton scattering amplitude. The method is based on an inte rference of the Bethe-Heitler and the virtual Compton scattering mecha nisms, generating an azimuthal asymmetry in the e(+) versus e-yield. T he general case of a circularly polarized beam and a longitudinally po larized target allows one to determine both the real and imaginary par ts of f(1) as well as f(2). The imaginary part of f(2) requires target polarization only. We calculate cross sections and asymmetries of the reaction p(gamma,e(+)e(-))p, estimate corrections and backgrounds, an d propose suitable kinematical regions to perform the experiment. Our investigation shows that photoproduction of e(+)e(-)-pairs off the pro ton and light nuclei may serve as a rather sensitive test of the valid ity of the Gerasimov-Drell-Hearn sum rule.