On the universality of cross sections of hadron–hadron (nuclei) collisions at superhigh energies

Abstract

We analyze the interplay of the hard and soft interaction dynamics in the onset of the black body limit in the high energy hadron–hadron and hadron–nucleus collisions. We demonstrate that hard interactions of large x partons with the strong small x gluon fields result in a faster increase of the range of the impact parameters where interaction reaches the unitarity limit. At superhigh energies, far above the Greizen–Zatsepin–Kuzmin limit, the radius of hadronic interactions, proportional to ln(s/s0), significantly exceeds static radii of the interacting hadrons (nuclei) and the dependence of the high energy elastic hadron–hadron scattering cross section on the impact parameter b becomes universal leading to the ratios of total cross sections of hadron–hadron, hadron–nucleus, nucleus–nucleus collisions becoming equal to one. The same universality is also expected for the ratio of structure functions: F2A(x,Q2)/F2N(x,Q2)→1 at very small x. We analyze how increase of the interaction radii with energy changes the energy dependence of total, absorption and inelastic cross sections, and the distribution over the number of wounded nucleons in proton–nucleus collisions.