Observation of deconfinement in a cold dense quark medium

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.

Comments: 6 pages, 4 figures