Dynamics of ultra-relativistic nuclear collisions with heavy beams: An experimental overview

Abstract

We review, from an experimental point of view, the current status of ultra-relativistic nuclear collisions with heavy beams.

Vector mesons in medium and dileptons in heavy-ion collisions

“…Other observables such as hadro-chemistry [31] or J/Ψ suppression [32] also support this scenario. Nonetheless, further data are essential to substantiate the present status and resolve the open questions.…”

Hadron production in central nucleus–nucleus collisions at chemical freeze-out

“…The thermal model was initially used for the AGS and SPS data [2] and was subsequently employed to describe data at SIS [3,4], SPS [5] and more recently at RHIC [6,7,8,9]. An analysis of the energy dependence of the thermal parameters extracted from fits of the experimental data, temperature (T ) and baryo-chemical potential (µ b ), established the "line of chemical freeze-out" [10]. These data were subsequently interpreted in terms of an universal condition for chemical freezeout [11].…”

“…These data were subsequently interpreted in terms of an universal condition for chemical freezeout [11]. Remarkably, it appears that at the top SPS energy the (T ,µ b ) values reach the phase boundary between the hadronic world and the quark-gluon plasma (QGP) [1,10], as calculated solving Quantum Chromo-Dynamics (QCD) on the lattice [12,13,14]. In this context, it has been argued that the QGP itself and the "deus ex machina" of phase space filling during hadronization are playing the crucial roles in achieving thermalization in high energy nucleus-nucleus collisions [15].…”

“…This makes the model a unique tool in the attempt to quantify from the experimental side the features of the phase diagram of hadronic matter [17,18,19]. Recent analyses over a broad energy range [20,21] have contributed in the on-going efforts to understand the chemical freeze-out criteria [1,10,11,22,23,24] in the phase diagram. It has been pointed out within a thermal model analysis that scanning the energy one encounters a transition from baryon-to meson-dominated freeze-out [25], with its associated fingerprint on the characteristics of hadron yields, also evidenced earlier [26].…”

On charm production near the phase boundary

“…Numerical solutions of QCD using lattice techniques imply that the critical temperature (at zero baryon density) is about 170 MeV [1]. Comprehensive surveys of the various experimental approaches on how to produce such matter in nucleusnucleus collisions have been given recently [2][3][4][5]. Here we focus on charm production and its recent interpretation in terms of a statistical hadronization model [6].…”