Measurement of the photon-proton total cross section at a center-of-mass energy of 209 GeV at HERA

Abstract The photon–proton total cross section has been measured in the process e + p → e + γp → e + X with the ZEUS detector at HERA. Events were collected with photon virtuality Q 2 2 and average γp center-of-mass energy W γp =209 GeV in a dedicated run, designed to control systematic effects, with an integrated luminosity of 49 nb −1 . The measured total cross section is σ tot γp =174±1 (stat.)±13 (syst.) μb. The energy dependence of the cross section is compatible with parameterizations of high-energy pp and p p data.