Unexpected properties of interaction of high-energy protons**This review is an extended version of a talk at the Scientific Session of the Physical Sciences Division, Russian Academy of Sciences, “On the 100th anniversary of the birth of Vitaly Ginzburg,” held on October 5, 20016 [see Physics-Uspekhi 60 (4) 413 (2017)

Abstract

Experimental data on proton–proton interactions in high-energy collisions show that the elastic-to-inelastic scattering ratio varies in an unexpected way with the collision energy: the decrease at comparatively low energies is followed by an increase by a factor of over 1.5 (!) in the energy range from 11–60 GeV at the Intersecting Storage Rings (ISR) to 7–13 TeV at the Large Hadron Collider (LHC). Intuitive expectations are that, classically, proton break-up processes continue increasing in number compared to proton survivals. It can be assumed that this surprising effect is due to either the asymptotic freedom property or the collision time being extremely short at such high energies. The unquestionable unitarity principle is combined with the available elastic scattering data to gain new insight into the spatial shape of the interaction region of colliding protons. We discuss how this region evolves at energies currently used and make some predictions on its behavior at still higher energies under different assumptions concerning the relative roles of elastic scattering and inelastic processes. The shape can transform rather drastically if elastic processes keep increasing in proportion. There is an unexpected corollary to this unexpected property. The possible origins of the effect and its relation to strong interaction dynamics are discussed.