Collective dynamics of the high-energy proton-nucleus collisions

TL;DR

This paper models proton-lead collisions at the LHC using a three-stage approach, successfully explaining collective phenomena like harmonic flow and ridge structures through initial fluctuations and hydrodynamics.

Contribution

It extends the three-stage relativistic hydrodynamic model to proton-nucleus collisions, demonstrating initial fluctuations as the source of observed collective flow.

Findings

Harmonic flow arises from initial event-by-event fluctuations.

The model reproduces observed elliptic flow coefficients.

Flow signals are robust against variations in viscosity and initial conditions.

Abstract

We analyze the proton-lead collisions at the LHC energy of 5.02TeV in the three-stage approach, previously used to successfully describe the relativistic A-A collisions. The approach consists of the early phase, modeled with the Glauber model, the event-by-event viscous 3+1 dimensional (3+1 D) relativistic hydrodynamics, and the statistical hadronization at freeze-out. We show that features typical of collective dynamics, such as the harmonic flow and the ridge structures in the two-particle correlations in relative azimuth and pseudorapidity, may be naturally explained in our framework. In the proton-nucleus system the harmonic flow is generated from an initially event-by-event deformed system and is entirely due to these initial fluctuations. Notably, fluctuations of strength of the initial Glauber sources which yield the observed distribution of hadron multiplicities and, at the same time, lead to correct values of the elliptic flow coefficients both from the two- and four-particle cumulant method, as measured by the ATLAS collaboration. The azimuthally asymmetric flow is not modified significantly when changing the viscosity coefficient, the initial time for the collective expansion, or the initial size of the fireball. The results present an estimate of the collective component in the two-particle correlations measured experimentally. We demonstrate that the harmonic flow coefficients can be experimentally measured with methods based on large rapidity gaps which reduce some of the other sources of correlations.