Signatures of collective behavior in small systems

TL;DR

This paper uses 3+1D viscous hydrodynamics to analyze collective behavior in small proton-nucleus collisions, confirming fluid-like properties and matching experimental flow measurements, thus supporting the fluid dynamics description of such systems.

Contribution

It demonstrates that hydrodynamics can accurately describe collective phenomena in small collision systems and explores the impact of initial state granularity on observables.

Findings

Hydrodynamics captures flow trends in pA and AA collisions.

Predictions for $r_n$ align with recent pA measurements.

Results are sensitive to initial state granularity.

Abstract

We perform 3+1D viscous hydrodynamics calculations of proton-nucleus (pA) and nucleus-nucleus (AA) collisions. Our goal is to understand the apparent collective behavior recently observed in pA collisions and to verify whether the highest multiplicity collision systems can be accurately described as a relativistic fluid. We compare our calculations of flow variables to existing measurements, and demonstrate that hydrodynamics correctly captures the measured trends. We show that our predictions for the pair correlation observable $r_n$ are validated by recent experimental pA measurements, and that our results are sensitive to the granularity of the initial state. We also compare our results with measurements done for nucleus-nucleus collisions.