Abstract
One important ingredient in the study of cosmological evolution is the equation of state of the primordial matter formed in the first stages of the Universe. It is believed that the first matter produced was of hadronic nature, probably the quark–gluon plasma which has been studied in high-energy collisions. There are several experimental indications of self-similarity in hadronic systems—in particular in multiparticle production at high energies. Theoretically, this property was associated with the dynamics of particle production, but it is also possible to relate self-similarity to the hadron structure—in particular to a fractal structure of this system. In doing so, it is found that the thermodynamics of hadron systems at equilibrium must present specific properties that are indeed supported by data. In particular, the well-known self-consistence principle proposed by Hagedorn 50 years ago is shown to be valid, and can correctly describe experimental distributions, mass spectrum of observed particles, and other properties of the hadronic matter. In the present work, a review of the theoretical developments related to the thermodynamical properties of hadronic matter and its applications in other fields is presented.
Highlights
One of the most striking features of high-energy collisions (HECs) is the formation of a system in thermodyanmical equilibrium which subsequently decays through the emission of several particles.In spite of the fact that evidence of the existence of such a system—which received the name “fireball”—was already present in the 1950s [1], the idea of fireballs was somewhat challenged by experimental data as the collision energy increased
A review of the theoretical developments related to the thermodynamical properties of hadronic matter and its applications in other fields is presented
Refs. [50,59,60,61,62,63,64] for recent works on the subject); the debate around the thermodynamical properties of the fireball formed at high energies continues
Summary
One of the most striking features of high-energy collisions (HECs) is the formation of a system in thermodyanmical equilibrium which subsequently decays through the emission of several particles. The predictions from Hagedorn’s theory were fully supported by data This success prompted many works in the following years: Frautshi [3], with his bootstrap model where hadrons are supposed to be made of hadrons—as is the case for fireballs—obtained the same mass spectrum formula firstly obtained by Hagedorn. Despite the astonishing success in predicting so many characteristics of the hot and dense hadronic matter, as the beam energy increased and a larger range of p T distribution became available, Hagedorn’s theory was found to fail in completely describing the outcome of HECs. Hagedorn himself proposed an alternative empirical model [7] in substitution to his thermodynamical theory. Only the hadronic matter is considered, so a phase transition to the quark–gluon plasma cannot be analysed
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