Proton–proton cross-sections: The interplay between density and radius

We argue that there are two mechanisms responsible for the growth of high energy cross-sections – image and image, say – in pp collisions. One is by the increase of matter density, resulting in the black disk saturation. The other is exclusively by radial expansion affecting the periphery of the overlap area. Within this simple model we can reproduce all available data in pp from ISR to LHC. In order to achieve a fast growth in the very high energy cosmic ray energies, we propose a fast black disk saturation followed by the dominance of geometric scaling (GS).