Thermalization in ultrarelativistic nuclear collisions. I. Parton kinetics and quark-gluon plasma formation

Abstract

A relativistic kinetic formulation of the time evolution of parton distributions during the early preequilibrium stage of nucleus-nucleus collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC) is presented to study the microscopic dynamics and equilibration of the system. The nuclear collision is described as a sequence of multiple hard and soft parton-parton collisions and associated parton emission and absorption processes. Important aspects for the space-time evolution of the partonic system are the balance between emissive and absorptive processes, dilated formation of gluon radiation, and the effects of soft gluon interference. The time evolution of central 32S+32S and 1 9 7 A~+ 1 9 7 A~ collisions at RHIC (fi = 200A GeV) is studied in complete phase space and the approach to equilibrium is investigated. The results obtained imply the formation of hot quark-gluon plasmas in these collisions with estimated equilibration times, temperatures, and energy densities of re, ~1 . 2 (1.8) fm/c, T 2.290 (325) MeV, and E ~1 7 (31) Gev/fm3 for 3 2~+ 3 2~ (197A~+197A~). The consequences of such rather high temperatures and energy densities should be clear quark-gluon plasma signatures, observable in the production of charm, strangeness, direct photons, and dileptons. PACS number(s): 25.75. +1, 12.38.Bx, 12.38.Mh, 24.85.f~

Melting hadrons, boiling quarks

“…How exactly this should work has never been shown: Among the first to address a parton based entropy production quantitatively within a kinetic collision model was Klaus Geiger [158,159] who built computer cascade models at parton level, and studied thermalization as a collision based process.…”

“…The lower is the energy of the bulls, the less we need to worry; the pancakes are not thin and one can try to make parton-collision cascade to describe the physics case, see e.g. Geiger-Sriwastava [154,158,159] for SPS energy range. The use of these methods for RHIC or even LHC energies looks less convincing [155].…”

“…To summarize, in the "low" energy regime of SPS we can try to build a parton cascade model to capture the essence of heavy-ion collision dynamics [158,159]. The understanding of the initial "formation" of QGP as a function of collision energy and the understanding of the mechanism that describe energy and baryon number stopping remains one of the fundamental challenges of the ongoing theoretical and experimental research program.…”

Strangeness chemical equilibration in a quark-gluon plasma

“…These effectively massless particles can be produced by entirely soft processes which are intrinsically non-perturbative [17]. Their chemical equilibration can be further driven by multi-particle collisions [18,19].…”

Triple-gluon and triple-quark elastic scatterings and early thermalization

“…Three-gluon to three-gluon scatterings have been shown to lead to rapid thermalization of gluon matter created in RHIC central Au-Au collisions [ 1]. Thermalization has been studied from parton cascade models [ 2,3,4] and in other model attempts [ 5,6,7,8,9,10,11,12].…”