Hot spots and the hollowness of proton-proton interactions at high energies

TL;DR

This paper explains the hollowness effect in high-energy proton-proton collisions as a consequence of gluonic hot spots expanding transversely with energy, leading to a depletion of inelasticity at zero impact parameter.

Contribution

It introduces a model using gluonic hot spots with correlations and multiple scatterings to explain the hollowness phenomenon at high energies.

Findings

Hollowness effect arises at 7 TeV due to hot spot growth.

The model reproduces the depletion of inelasticity density at zero impact parameter.

Hot spot correlations are crucial for the effect's emergence.

Abstract

We present a dynamical explanation of the hollowness effect observed in proton-proton scattering at $\sqrt s\!=\!7$ TeV. This phenomenon, not observed at lower energies, consists in a depletion of the inelasticity density at zero impact parameter of the collision. Our analysis is based on three main ingredients: we rely gluonic hot spots inside the proton as effective degrees of freedom for the description of the scattering process. Next we assume that some non-trivial correlation between the transverse positions of the hot spots inside the proton exists. Finally we build the scattering amplitude from a multiple scattering, Glauber-like series of collisions between hot spots. In our approach, the onset of the hollowness effect is naturally explained as due to the diffusion or growth of the hot spots in the transverse plane with increasing collision energy.