How big are the smallest drops of quark-gluon plasma?

TL;DR

This paper uses holographic duality to study the formation and size of quark-gluon plasma droplets in high-energy collisions, showing hydrodynamics applies even at microscopic scales.

Contribution

It provides the first holographic analysis of small, strongly coupled plasma droplets formed in shock wave collisions, linking their size to the effective temperature.

Findings

Droplet size scales as inverse of effective temperature

Hydrodynamics accurately describes plasma evolution at microscopic scales

Supports hydrodynamics applicability in small collision systems

Abstract

Using holographic duality, we present results for both head-on and off-center collisions of Gaussian shock waves in strongly coupled $\mathcal N = 4$ supersymmetric Yang-Mills theory. The shock waves superficially resemble Lorentz contracted colliding protons. The collisions results in the formation of a plasma whose evolution is well described by viscous hydrodynamics. The size of the produced droplet is $R \sim 1/T_{\rm eff}$ where $T_{\rm eff}$ is the effective temperature, which is the characteristic microscopic scale in strongly coupled plasma. These results demonstrate the applicability of hydrodynamics to microscopically small systems and bolster the notion that hydrodynamics can be applied to heavy-light ion collisions as well as some proton-proton collisions.