Total Photoabsorption Cross Sections up to 18 GeV and the Nature of Photon Interactions

Abstract

The smallness of nucleon photoabsorption would imply total photonucleus cross sections which vary as the number of nucleons in the nucleus, but if $\rho$ dominance is correct the resulting strong interactions would take place primarily with the surface nucleons. At Stanford Linear Accelerator Center we have measured the photoabsorption in H, D, C, Cu, and Pb and have found cross sections which vary as $\sim A^{0.9}$ indicating that the photon interacts, at least partially, as a strongly interacting particle.