a Measurement of the Total Photon-Proton Cross Section in the Center of Mass Energy Range 167 TO 194 GEV

The thesis is a complete presentation of a total photon-proton (gamma p) cross section measurement using the ZEUS detector at the recently commissioned HERA electron-proton (ep) collider. A measurement of gamma p interactions using the exchanged virtual photon of ep collisions is shown to be justified and the correct flux of photons is determined. HERA and ZEUS are introduced, with an emphasis on the components used in the measurement. The data was collected during the fall of 1992 for which the experimental conditions are described, including the determination of the 13 nb ^{-1} of integrated ep luminosity which provided the event sample. The treatment of background events is described, as are event losses due to inefficiencies in their identification by the trigger and in their subsequent analysis. The observed number of events is corrected for the acceptance of the experiment using Monte Carlo simulations of gamma p interactions tuned to match characteristics of the observed events. Radiative corrections to the measurement are shown to be small and the calculation is corroborated by a measurement of the number of radiative events. In the gamma p center of mass energy range 167 < W < 194 GeV, the total gamma p cross section is sigma _sp{rm tot}{gamma p} = 143 +/- 3 (stat.) +/- 18 (syst.) mub.