Energy evolution of proton shapes

The shape and darkness of the interaction region for colliding protons change as their energies increase. The ratio of the diffraction-cone slope to the total cross section is a crucial parameter here. Experimental data at different energies are indicative of its energy evolution. It is shown that the darkness of the proton interaction region in central collisions is fully governed by this parameter. At LHC energies, the interactions become completely absorptive at small impact parameters. This results in interesting predictions for inelastic processes (especially, for dijet production). A lower limit on the ratio in question is determined. This imposes some restrictions on its energy behavior. Its effect on the differential cross section outside the diffraction cone is discussed. It is shown that the real part of the amplitude becomes very important there at the LHC energies, its sign being opposite to the sign of the imaginary part. It is argued that the black-disk limit is not reached at present-day energies, but that it can probably be approached at extremely high energies. However, the structure of the interaction region in this limiting case reminds a torus rather than a black disk.