Irreversibility, steady state, and non-equilibrium physics in relativistic heavy ion collisions

TL;DR

This paper discusses how heavy ion collisions at ultrarelativistic energies demonstrate irreversibility and steady states, challenging traditional equilibrium assumptions and impacting the interpretation of hadron yields and spectra.

Contribution

It introduces the concept that heavy ion collision systems evolve towards steady states rather than equilibrium, providing a new perspective on modeling such processes.

Findings

Heavy ion collisions exhibit irreversibility and steady states.

Traditional thermal models struggle to accurately describe hadron yields.

Microscopic models confirm the absence of pure equilibrium states.

Abstract

Heavy ion collisions at ultrarelativistic energies offer the opportunity to study the irreversibility of multiparticle processes. Together with the many-body decays of resonances, the multiparticle processes cause the system to evolve according to Prigogine's steady states rather than towards statistical equilibrium. These results are general and can be easily checked by any microscopic string-, transport-, or cascade model for heavy ion collisions. The absence of pure equilibrium states sheds light on the difficulties of thermal models in describing the yields and spectra of hadrons, especially mesons, in heavy ion collisions at bombarding energies above 10 GeV/nucleon.