Collective flow and viscosity in relativistic heavy-ion collisions

TL;DR

This paper reviews how collective flow phenomena and their fluctuations in relativistic heavy-ion collisions help determine the quark-gluon plasma's shear viscosity, drawing parallels with early universe conditions.

Contribution

It provides a comprehensive review of collective flow analysis and viscosity extraction methods in heavy-ion collisions, highlighting recent experimental insights.

Findings

Shear viscosity of QGP is close to the quantum lower bound.

Flow anisotropies are sensitive to initial state fluctuations.

Experimental data supports nearly perfect fluid behavior of QGP.

Abstract

Collective flow, its anisotropies and its event-to-event fluctuations in relativistic heavy-ion collisions, and the extraction of the specific shear viscosity of quark-gluon plasma (QGP) from collective flow data collected in heavy-ion collision experiments at RHIC and LHC are reviewed. Specific emphasis is placed on the similarities between the Big Bang of our universe and the Little Bangs created in heavy-ion collisions.