Vector meson cross sections at HERA

Fig. 1. Schematic picture of inelastic (a) and elastic (b) vector meson leptoproduction Vector mesons can be produced in two different ways in lepton proton scattering, in so-called inelastic processes, where the proton breaks, or elastic (exclusive) processes, where the incoming proton stays intact. The different production mechanisms are shown schematically in Fig. 1. They suggest that the cross section for inelastic vector meson production behaves like σinel ∼ xG(x, μ 2) whereas for elastic production like σel ∼ [ xG(x, μ2) 2 . Different regions of the available phase space ranging from photoproduction (Q2 ∼ 0) to the DIS regime (Q2 > 1 GeV2) and various vector mesons, including photons can be investigated.