Free Quarks and Gluons
The current theory of the strong interaction (called Quantum Chromo-Dynamics) predicts that at very high temperatures and very high densities, quarks and gluons should no longer be confined inside composite particles. Instead they should exist freely in a new state of matter known as quark-gluon plasma.
Such a transition should occur when the temperature exceeds a critical value estimated to be around 2 000 billion degrees... about 100 000 times hotter than the core of the Sun! Such temperatures have not existed in Nature since the birth of the Universe. We believe that for a few millionths of a second after the Big Bang the temperature was indeed above the critical value, and the entire Universe was in a quark-gluon plasma state.
The two heavy nuclei approach each other at a speed close to that of light. According to Einstein’s theory of relativity, they appear as very thin discs.
The nuclei collide and the extreme temperature releases the quarks (red, blue and green) and the gluons.
Quarks and gluons collide with each other creating a thermally equilibrated environment: the quark–gluon plasma.
The plasma expands and cools down to the temperature (10¹² degrees) at which quarks and gluons regroup to form ordinary matter, barely 10-23 seconds after the start of the collision.
The thousands of new particles created in this way move towards the detection system (simulation by H. Weber, UrQMD, Frankfurt).