When the entire universe was about 10^-6 seconds old, its density and composition were the same as the inside of a proton or neutron today. Protons and neutrons are like condensed droplets of this original "quark-gluon" plasma that once filled the entire universe. This is somewhat analogous to the fact that the interior of a modern living cell is in many ways a highly evolved miniature drop of the ancient "organic" ocean in the era long before atmospheric oxygen appeared. Physicists realized in the 1980s that synchrotrons accelerating heavy nuclei in colliding beams should be able for a split second to recreate this quark-gluon plasma, for study in the laboratory... our only hope of getting a sample to study, here on earth, of the universe at the tender age of a millionth of a second. Such experiments were soon being carried out at facilities like RHIC and the LHC.

The chemical potential is the density of baryons minus the density of antibaryons.

There was an unexpected setback, in that a first-order phase transition to the quark-gluon plasma could not be seen at either RHIC or LHC, because of a critical point in the phase diagram! However, new accelerators were already under construction, one of which has antimatter beams, that by foresighted design access the newly defined phase transition region. These accelerators, FAIR in Germany, and NICA in Russia, are set to become operational in the very near future. [Of course they have many other uses than making quark-gluon plasma, such as making nuclei extremely far off the line of stability.  The masses of such nuclei are badly needed by astrophysicists working on neutron star-neutron star collisions.]