![quark gluon plasma quark gluon plasma](https://physics.aps.org/assets/885f79ba-ee3d-497e-84f3-dedfb2cb0d85/e86_1_thumb.png)
It has never been observed yet, though lots of people are thinking about options to tune collision parameters such that it could be created, and about possible signals in the late hadronic data. OK, Colour-Superconductivity is, so far, not more than a theoretical prediction from QCD. I don't quite understand? Well, the same constituents, quarks and gluons, can form a "liquid" or gas at high temperture, and a "condensate" (Colour-Superconducitvity) at high density and moderate temperature. It is sure to note that a hot Plasma (phase of matter), can be of the same constituency of a cold Plasma (Bose_Einstein_Condensate) ?
#Quark gluon plasma plus
In a hot QGP, the net density of quarks (quarks minus antiquarks) is very low, while the number density (quarks plus antiquarks) is very high, and comparable to the density of a cool, compressed QGP. Here, one has to be careful about what is meant with density of quarks, since we deal with a highly relativistic system. Is the density of "Hot" Quark/Gluons, equal to that of "Cold" Quark/Gluons?
#Quark gluon plasma free
On the other hand, by heating, one goes through a cross-over form hadrons to a QGP, which means that there is a smooth change in the proprties of the particles, from hadrons to (maybe) QGP liquid to free QGP gas. Current wisdom ist that you can reach the QGP at moderate temperature also if you just compress enough. So, indeed, the picture shows cool, compressed nuclear matter, rather than a hot quark gluon gas. I guess I should write sometime something about the phase diagram of nuclear matter. Virtual Gas = Virtual Solid = Virtual Liquids, for High temperatures, just as for Cold temperatures? However, from models that analyse the collisions and interactions of partons (the quarks and gluons in the nuclei), it looks as if even this short time can be enough to create an equilibrated system, which then, of course, expands and cools extremely rapidly. It is not self-evident that it makes sense at all to speak of quark matter in equilibrium in connection with heavy ion collisions. Good point: The picture shows some static, equilibrium configuration, while a real collision is an extremely fast process - it takes only some Fermi/c, or the time for light to cross a large nucleus. Not really capture though, the fact that a new phase of matter at specific temperature, is an intermediate product? Otherwise I don't understand, I have to admit. (picture credits go to Jens Berger, from the STAR team) The tracks of the charged particles are measured in the large detectors, and they typically look like this: In a head-on, central collision with such an energy, some 1000 particles are produced. Such a gold nucleus consists of 197 nucleons (79 protons and 118 neutrons), which adds up to 40 TeV: that is roughly the energy of a mass of 10 milligram (a grain of coarse salt) falling from a height of 2.5 cm (or 1 inch), its macroscopic! The top energy for the collision of gold nuclei at RHIC is about 200 GeV per nucleon. The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) performs such experiments, with which we hope re-create conditions similar to those in the very early universe.
![quark gluon plasma quark gluon plasma](https://blackwells.co.uk/jacket/l/9788184874075.jpg)
For this purpose, heavy nuclei like those of lead and gold, are collided with highest energies and form an intermediate hot and dense state, the so-called fireball.
![quark gluon plasma quark gluon plasma](https://i1.sndcdn.com/artworks-000099771839-mu50it-t500x500.jpg)
The possibility to produce a state of matter as hot and dense as it was in the first moments of the universe is one of the primary goals for Heavy Ion collisions.