It is shown that the universality of the initial and final state interactions responsible for the transition between the on-- and off--mass shell states leads to the energy independence of the ratio of exclusive $\rho$ electroproduction cross section to the total cross section. It is demonstrated that the above universality and explicit mass dependence of the exponent in the power--like energy behavior of the cross-section obtained in the approach based on unitarity is in a quantitative agreement with the high--energy HERA experimental data. We discuss also HERA results on angular distributions of vector--meson production.
Categories: hep-ph