Observation of deconfinement in a cold dense quark medium

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 $a=0.044\mathrm{f}\mathrm{m}$. This small lattice spacing allowed us to reach very large baryon density (up to quark chemical potential $\mu_q > 2000 $\mathrm{M}\mathrm{e}\mathrm{V}$$)avoidingstronglatticeartifacts\mathrm{.}Intheregion$\mu_q\sim 1000 $\mathrm{M}\mathrm{e}\mathrm{V}$$ 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{M}\mathrm{e}\mathrm{V}$$, we observe a monotonous decrease of the spatial string tension ${\sigma }_s$ which ends up with ${\sigma }_s$ vanishing at $\mu_q > 2000 $\mathrm{M}\mathrm{e}\mathrm{V}$$. 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.