Chiral Effects in Nucleus–Nucleus Collisions: Experimental Review

A survey of experimental results obtained by studying chiral effects in nucleus–nucleus collisions at various energies is presented. The entire body of these experimental results confirms indirectly a topologically nontrivial structure of the QCD vacuum and the possibility of a local violation of discrete QCD symmetries at finite temperature. A significant decrease in the asymmetry of the distribution of electrically charged particles with respect to the reaction plane in heavy-ion collisions in the energy range of $\sqrt{sNN}$ GeVmay be indicative of a possible transition to the region where hadron states dominate over quark–gluon degrees of freedom in a mixed phase formed in nucleus–nucleus collisions at intermediate energies.