Total ${\gamma }^{\ast }$ p Cross Section

Abstract

This paper shows that the approach based on Gribov's ideas for the photon-proton interaction, is able to describe the experimental data over a wide range of photon virtualities $Q^2=0-100Ge{V}^2$ and energies $\sqrt{s}=W=3-300GeV$. A simple model is suggested which provides a quantitative way of describing the matching between short and long distances (between "soft" and "hard" processes) in photon-proton interaction at high energy. The main results of our analysis are: (i) the values of the separation parameters differentiating the "soft" and "hard" interactions are determined; (ii) the additive quark model can be used to calculate the "soft" contribution to the photon - proton interaction; (iii) a good description of the ratio ${\sigma }_L/{\sigma }_T$ is obtained ; and (iv) a considerable contribution of the "soft" process at large $Q^2$, and of "hard" processes at small $Q^2$ was found.

Comments: 20 pages in latex.file,9 figures in eps and ps files