Observation of deconfinement in a cold dense quark medium

TL;DR

This study uses lattice QCD simulations to observe the confinement/deconfinement transition at high baryon densities, revealing a transition to a weakly interacting quark-gluon plasma distinct from high-temperature cases.

Contribution

First lattice QCD simulation to identify confinement/deconfinement transition at very high baryon densities with zero temperature.

Findings

Confinement/deconfinement transition occurs at quark chemical potential > 1000 MeV.

String tension vanishes at high density, indicating deconfinement.

High-density quark-gluon plasma behaves as a weakly interacting gas.

Abstract

In this paper we study the confinement/deconfinement transition in lattice $SU(2)$ QCD at finite quark density and zero temperature. The simulations are performed on an $32^4$ lattice with rooted staggered fermions at a lattice spacing $a = 0.044 \mathrm{~fm}$. This small lattice spacing allowed us to reach very large baryon density (up to quark chemical potential $\mu_q > 2000 \mathrm{~MeV}$) avoiding strong lattice artifacts. In the region $\mu_q\sim 1000 \mathrm{~MeV}$ we observe for the first time the confinement/deconfinement transition which manifests itself in rising of the Polyakov loop and vanishing of the string tension $\sigma$. After the deconfinement is achieved at $\mu_q > 1000 \mathrm{~MeV}$, we observe a monotonous decrease of the spatial string tension $\sigma_s$ which ends up with $\sigma_s$ vanishing at $\mu_q > 2000 \mathrm{~MeV}$. From this observation we draw the conclusion that the confinement/deconfinement transition at finite density and zero temperature is quite different from that at finite temperature and zero density. Our results indicate that in very dense matter the quark-gluon plasma is in essence a weakly interacting gas of quarks and gluons without a magnetic screening mass in the system, sharply different from a quark-gluon plasma at large temperature.