Diagnostics of superdense matter in ultrarelativistic nuclear collisions

Abstract

This review presents an overview of the methods of detecting and determining the main parameters of superdense hadronic matter created in ultrarelativistic nuclear collisions. Questions related to the quark–hadron phase transition and the conditions under which it is realized are discussed, and various approaches to describing the evolution of nucleus–nucleus collisions are analyzed: microscopic Monte Carlo generators and hydrodynamical models. The basic tests proposed for the experimental study of the properties of nuclear matter under extreme conditions are studied. Possible interpretations are given of the features observed in experiments on relativistic nuclear collisions at existing accelerators (AGS, SPS), compared with the corresponding hadron–hadron collisions: broadening of the hadron momentum spectra, increased yield of low-mass dileptons, enhanced strange-particle production, suppression of the Ψ-resonance yield, and so on. The prospects for future experiments at the RHIC and LHC colliders are discussed. Special attention is paid to hard probes, which give information about the early stages of evolution of the hot, strongly interacting matter. Model representations are used to analyze the effects expected as a result of the passage of hard jets of color-charged partons through the dense matter, and the matter parameters primarily affecting the jet characteristics and their experimental identification are determined. The question of identifying hard QCD jets in heavy-ion collisions on the background of large statistical fluctuations of the transverse energy flow due to the large secondary-particle multiplicity is also discussed.