The central issue of the formation of a quark–gluon plasma is the research for the onset of deconfinement. From the beginning of the research on formation of QGP, the issue was whether energy density can be achieved in nucleus-nucleus collisions. This depends on how much energy each nucleon loses. An influential reaction picture was the scaling solution presented by Bjorken. This model applies to ultra-high energy collisions. In experiments carried out at CERN SPS and BNL RHIC more complex situation arose, usually divided into three stages:
* Primary parton collisions and baryon stopping at the time of complete overlapping of the colliding nuclei.
* Redistribution of particle energy and new particles born in the QGP fireball.
* The fireball of QGP matter equilibrates and expands before hadronizing.
More and more experimental evidence points to the strength of QGP formation mechanisms—operating even in LHC-energy scale proton-proton collisions.