Total and jet photoproduction cross sections at DESY HERA and Fermilab energies

We present results of calculations of the total and jet photon-proton cross sections at energies of relevance to the Fermilab E683 experiment and the ZEUS and H-1 experiments at the DESY ep collider HERA. The calculations take into account the high-energy QCD structure of the photon and are performed for two different photon structure functions. We discuss how these forthcoming experiments may be able to provide important information on two major uncertainties inherent to the calculation of photoproduction cross sections in particular and in a more general context, to the nature of strong interactions. If the total photoproduction cross section is measured at E683 energies (√s =16–28 GeV), it will provide a firmer value for ${\mathit{p}}_{\mathit{T}}^{\min }$, the lower bound on the transverse momentum of outgoing jets, which signals the onset of hard scattering. At HERA energies (√s up to 300 GeV), the total and jet cross sections will help determine the photon structure function better at low-x (the fractional parton momentum) values, currently a region where there are large uncertainties due to a lack of data.