Evidence for Hydrodynamic Evolution in Proton-Proton Scattering at LHC Energies

TL;DR

This paper presents evidence that hydrodynamic models, typically used for heavy ion collisions, are applicable to high-multiplicity proton-proton collisions at LHC energies, suggesting thermalization occurs in such events.

Contribution

It introduces a hydrodynamic evolution framework for high-multiplicity $pp$ collisions, supported by Bose-Einstein correlation data at LHC energies.

Findings

High energy densities in $pp$ collisions support hydrodynamic behavior.

Bose-Einstein correlations indicate possible thermalization.

Hydrodynamic models can describe high-multiplicity $pp$ events.

Abstract

In $pp$ scattering at LHC energies, large numbers of elementary scatterings will contribute significantly, and the corresponding high multiplicity events will be of particular interest. Elementary scatterings are parton ladders, identified with color flux-tubes. In high multiplicity events, many of these flux tubes are produced in the same space region, creating high energy densities. We argue that there are good reasons to employ the successful procedure used for heavy ion collisions: matter is assumed to thermalizes quickly, such that the energy from the flux-tubes can be taken as initial condition for a hydrodynamic expansion. This scenario gets spectacular support from very recent results on Bose-Einstein correlations in $pp$ scattering at 900 GeV at LHC.