Small System Collectivity in Relativistic Hadron and Nuclear Collisions

TL;DR

This paper reviews the discovery of fluid-like collective behavior in small collision systems, challenging previous notions that such phenomena only occur in large, hot nuclear matter.

Contribution

It highlights recent experimental findings of collective effects in small systems and discusses their implications for understanding quark-gluon plasma formation.

Findings

Collective flow observed in small systems like p+p and p+A collisions.

Fluid-like behavior extends to smaller, less energetic collision systems.

Implications for the universality of quark-gluon plasma formation.

Abstract

The bulk motion of nuclear matter at the ultra-high temperatures created in heavy-ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider is well described in terms of nearly inviscid hydrodynamics, thereby establishing this system of quarks and gluons as the most perfect fluid in nature. A revolution in the field is underway, spearheaded by the discovery of similar collective, fluid-like phenomena in much smaller systems including p+p, p+A, d+Au, and $^3$He$+$Au collisions. We review these exciting new observations and their implications.