Total Hadronic Cross Section ofγRays in Hydrogen in the Energy Range 0.265-4.215 GeV

The total cross section of $\gamma$ rays in hydrogen resulting in hadron production, ${\sigma }_T$, has been measured over the energy range 265-4215 MeV. A tagging system with narrow energy bins was employed. Structure in the resonance region followed by a steady fall with energy has been observed and the results are analyzed. The forward amplitude of $\gamma$-proton scattering is evaluated, and its behavior in the Argand diagram studied as a function of energy. The relationships of the measurements to Regge-pole theory and the vector-dominance model are detailed.