The quark — gluon medium
Lebedev Physical Institute, Russian Academy of Sciences, Leninsky prosp. 53, Moscow, 119991, Russian Federation
The properties of the quark — gluon medium observed
in high-energy nucleus — nucleus collisions are discussed. The
main experimental facts about these collisions are briefly described and compared with data about proton — proton collisions.
Both microscopic and macroscopic approaches to their description are reviewed. The chromodynamics of the quark — gluon
medium at high energies is mainly considered. The energy loss
of partons moving in this medium is treated. The principal
conclusion is that the medium possesses some collective properties which are crucial for understanding the experimental observations.