Collectivity without plasma in hadronic collisions

TL;DR

This paper introduces a microscopic model for collective effects in high multiplicity proton-proton collisions, where overlapping QCD strings generate transverse pressure and flow, explaining the observed azimuthal correlations without requiring a quark-gluon plasma.

Contribution

The model incorporates transverse string extension and pressure effects into PYTHIA8, providing a novel explanation for collective phenomena in proton-proton collisions.

Findings

Qualitatively reproduces the near-side ridge in high multiplicity events

Suggests collective effects can arise without a deconfined plasma

Highlights importance of string interactions in small systems

Abstract

We present a microscopic model for collective effects in high multiplicity proton--proton collisions, where multiple partonic subcollisions give rise to a dense system of strings. From lattice calculations we know that QCD strings are transversely extended, and we argue that this should result in a transverse pressure and expansion, similar to the flow in a deconfined plasma. The model is implemented in the PYTHIA8 Monte Carlo event generator, and we find that it can qualitatively reproduce the long range azimuthal correlations forming a near-side ridge in high multiplicity proton--proton events at LHC energies.