Color evaporation and elastic [ípsilon] photoproduction at DESY HERA

Abstract

The diffractive photoproduction of vector mesons is usually described by considering the two-gluon (Pomeron) exchange, the nondiagonal parton distributions, and the contribution of the real part to the cross section. In this Brief Report we analyze the diffractive photoproduction of the Y at DESY HERA using an alternative model, the color evaporation model (CEM), where the cross section is simply determined by the boson-gluon cross section and an assumption for the production of the colorless state. We verify that, as in the J/Ψ case, the HERA data for this process can be well described by the CEM. Moreover, we propose the analysis of the ratio R=σY /σJ/Ψ to discriminate between the different approaches.