7 Relativistic Nucleus-Nucleus Collisions and the QCD Matter Phase Diagram
317
flow (Sect. 7.4), high p T and jet quenching (Sect. 7.5) and quarkonium suppression
(Sect. 7.6) as well as in-medium -meson “melting”. We then turn to the late period,
with correlation and fluctuation studies (Sect. 7.7). We conclude (Sect. 7.8) with a
summary, including an outlook to the future of the research field.
However, before turning to such specific observables we shall continue this
introductory chapter, with a look at the origin, and earlier development of the ideas
that have shaped this field of research (Sect. 7.1.2). Then we turn to a detailed
description of the overall dynamical evolution of relativistic nucleus-nucleus collisions, and to the typical overall patterns governing the final distributions in
transverse and longitudinal (rapidity) phase space (Sect. 7.2). The aspects of an
approach toward equilibrium, at various stages of the dynamical evolution (which
are of key importance toward the intended elucidation of the QCD matter phase
diagram), will be considered, in particular.
7.1.2 History
The search for the phase diagram of strongly interacting matter arose in the 1960s,
from a coincidence of ideas developing—at first fairly independently—in nuclear
and astrophysics. In fact, the nuclear proton-neutron matter, a quantum liquid at
T = 0 and energy density = 0.15 GeV/fm 3 , represents the ground state of
extended QCD matter. Of course, QCD was unknown during the development
of traditional nuclear physics, and the extended matter aspects of nuclei—such
as compressibility or the equation of state, in general—did not receive much
attention until the advent, in the 1960s, of relativistic nuclear mean field theory,
notably s-matrix theory by Brueckner [26] and the σ -model of Walecka [27]. These
theories developed the novel view of “infinite nuclear matter” structure, based on
in-medium properties of the constituent baryons that share parts of their vacuum
mass and surface structure with the surrounding, continuous field of relativistic
scalar and vector mesons. Most importantly, in the light of subsequent development,
these theories allowed for a generalization away from ground state density and
zero temperature. Such developments turned out to be of key relevance for acute
nuclear astrophysics problems: the dynamics of type II super-novae and the stability
of neutron stars, which both required the relation of pressure to density and
temperature of hadronic matter, i.e. the hadronic matter equation of state (EOS).
H.A. Bethe et al. [28] postulated that the final stages of supernova collapse should
evolve through the density interval 0.1 ≤ // 0 ≤ 5 where 0 = 0.16 (baryons
per fm 3 ) is the nuclear matter ground state density, and a similar domain was
expected for the neutron star density variation from surface to interior [29]. It
was clear that, at the highest thus considered densities the EOS might soften due
to strange hadron production caused by increasing Fermi energy. However the
field theoretical models permitted no reliable extrapolation to such high densities
(which, in retrospect, are perhaps not reached in supernova dynamics [30]), and the
experimental information concerning the EOS from study of the giant monopole
317
flow (Sect. 7.4), high p T and jet quenching (Sect. 7.5) and quarkonium suppression
(Sect. 7.6) as well as in-medium -meson “melting”. We then turn to the late period,
with correlation and fluctuation studies (Sect. 7.7). We conclude (Sect. 7.8) with a
summary, including an outlook to the future of the research field.
However, before turning to such specific observables we shall continue this
introductory chapter, with a look at the origin, and earlier development of the ideas
that have shaped this field of research (Sect. 7.1.2). Then we turn to a detailed
description of the overall dynamical evolution of relativistic nucleus-nucleus collisions, and to the typical overall patterns governing the final distributions in
transverse and longitudinal (rapidity) phase space (Sect. 7.2). The aspects of an
approach toward equilibrium, at various stages of the dynamical evolution (which
are of key importance toward the intended elucidation of the QCD matter phase
diagram), will be considered, in particular.
7.1.2 History
The search for the phase diagram of strongly interacting matter arose in the 1960s,
from a coincidence of ideas developing—at first fairly independently—in nuclear
and astrophysics. In fact, the nuclear proton-neutron matter, a quantum liquid at
T = 0 and energy density = 0.15 GeV/fm 3 , represents the ground state of
extended QCD matter. Of course, QCD was unknown during the development
of traditional nuclear physics, and the extended matter aspects of nuclei—such
as compressibility or the equation of state, in general—did not receive much
attention until the advent, in the 1960s, of relativistic nuclear mean field theory,
notably s-matrix theory by Brueckner [26] and the σ -model of Walecka [27]. These
theories developed the novel view of “infinite nuclear matter” structure, based on
in-medium properties of the constituent baryons that share parts of their vacuum
mass and surface structure with the surrounding, continuous field of relativistic
scalar and vector mesons. Most importantly, in the light of subsequent development,
these theories allowed for a generalization away from ground state density and
zero temperature. Such developments turned out to be of key relevance for acute
nuclear astrophysics problems: the dynamics of type II super-novae and the stability
of neutron stars, which both required the relation of pressure to density and
temperature of hadronic matter, i.e. the hadronic matter equation of state (EOS).
H.A. Bethe et al. [28] postulated that the final stages of supernova collapse should
evolve through the density interval 0.1 ≤ // 0 ≤ 5 where 0 = 0.16 (baryons
per fm 3 ) is the nuclear matter ground state density, and a similar domain was
expected for the neutron star density variation from surface to interior [29]. It
was clear that, at the highest thus considered densities the EOS might soften due
to strange hadron production caused by increasing Fermi energy. However the
field theoretical models permitted no reliable extrapolation to such high densities
(which, in retrospect, are perhaps not reached in supernova dynamics [30]), and the
experimental information concerning the EOS from study of the giant monopole