https://www.arxiv.org/pdf/nucl-ex/0501009

Experimental and theoretical challenges in the search for the quark-gluon plasma: The STAR Collaboration's critical assessment of the evidence from RHIC collisions

http://nuclear.korea.ac.kr/~bhong/class/WhitePaper_PHENIX_RUN1-3.pdf

Formation of dense partonic matter in relativistic nucleus–nucleus collisions at RHIC: Experimental evaluation by the PHENIX Collaboration

http://nuclear.korea.ac.kr/~bhong/class/WhitePaper_BRAHMS_RUN1-3.pdf

Quark gluon plasma and color glass condensate at RHIC? The Perspective from the BRAHMS experiment

New forms of QCD matter discovered at RHIC

The current status of theoretical studies on the quantum chromodynamics (QCD) phase diagram at finite temperature and baryon chemical potential is reviewed with special emphasis on the origin of various phases and their symmetry breaking patterns. Topics include quark deconfinement, chiral symmetry restoration, order of the phase transitions, QCD critical point(s), colour superconductivity, various inhomogeneous states and implications from QCD-like theories.

https://iopscience.iop.org/article/10.1088/0034-4885/74/1/014001/pdf

The phase diagram of dense QCD

We argue that the emission of hadrons with transverse momentum up to about 5 GeV/c in central relativistic heavy ion collisions is dominated by recombination, rather than fragmentation of partons. This mechanism provides a natural explanation for the observed constant baryon-to-meson ratio of about one and the apparent lack of a nuclear suppression of the baryon yield in this momentum range. Fragmentation becomes dominant at higher transverse momentum, but the transition point is delayed by the energy loss of fast partons in dense matter.

https://arxiv.org/pdf/nucl-th/0301087.pdf

Hadronization in Heavy-Ion Collisions: Recombination and Fragmentation of Partons

We discuss hadron production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) We argue that hadrons at transverse momenta ${P}_{T}l5\phantom{\rule{03em}{0ex}}\text{GeV}$ are formed by recombination of partons from the dense parton phase created in central collisions at RHIC We provide a theoretical description of the recombination process for ${P}_{T}g2\phantom{\rule{03em}{0ex}}\text{GeV}$ Below ${P}_{T}=2\phantom{\rule{03em}{0ex}}\text{GeV}$ our results smoothly match a purely statistical description At high transverse momentum hadron production is well described in the language of perturbative QCD by the fragmentation of partons We give numerical results for a variety of hadron spectra, ratios, and nuclear suppression factors We also discuss the anisotropic flow ${v}_{2}$ and give results based on a flow in the parton phase Our results are consistent with the existence of a parton phase at RHIC hadronizing at a temperature of $175\phantom{\rule{03em}{0ex}}\text{MeV}$ and a radial flow velocity of $055c$

Hadron production in heavy ion collisions: Fragmentation and recombination from a dense parton phase

We introduce a combined, fully three-dimensional macroscopic/microscopic transport approach employing relativistic 3D hydrodynamics for the early, dense, deconfined stage of the reaction and a microscopic nonequilibrium model for the later hadronic stage where the equilibrium assumptions are no longer valid. Within this approach, we study the dynamics of hot bulk QCD matter, which is being created in ultrarelativistic heavy-ion collisions at the BNL Relativistic Heavy-Ion Collider. Our work is an extension of the well-known hybrid macro+micro approach in 1+1 and 2+1 dimensions, which is capable of self-consistently calculating the freeze-out of the hadronic system while accounting for the collective flow on the hadronization hypersurface generated by the quark-gluon plasma expansion. In particular, we perform a detailed analysis of the reaction dynamics, hadronic freeze-out, and transverse flow.

https://arxiv.org/pdf/nucl-th/0607018.pdf

Space-time evolution of bulk QCD matter

We perform a systematic comparison of three different jet energy-loss approaches. These include the Armesto-Salgado-Wiedemann scheme based on the approach of Baier-Dokshitzer-Mueller-Peigne-Schiff and Zakharov (BDMPS-Z/ASW), the higher twist (HT) approach and a scheme based on the Arnold-Moore-Yaffe (AMY) approach. In this comparison, an identical medium evolution will be utilized for all three approaches: this entails not only the use of the same realistic three-dimensional relativistic fluid dynamics (RFD) simulation, but also the use of identical initial parton-distribution functions and final fragmentation functions. We are, thus, in a unique position to not only isolate fundamental differences between the various approaches but also make rigorous calculations for different experimental measurements using state of the art components. All three approaches are reduced to versions containing only one free tunable parameter, this is then related to the well-known transport parameter $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}$. We find that the parameters of all three calculations can be adjusted to provide a good description of inclusive data on ${R}_{\mathit{AA}}$ vs transverse momentum. However, we do observe slight differences in their predictions for the centrality and azimuthal angular dependence of ${R}_{\mathit{AA}}$ vs ${p}_{T}$. We also note that the values of the transport coefficient $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}$ in the three approaches to describe the data differ significantly.

Systematic comparison of jet energy-loss schemes in a realistic hydrodynamic medium

This is a pedagogical review of the lattice study of finite density QCD. It is intended to provide the minimum necessary content, so that it may be used as an introduction for newcomers to the field and also for those working in nonlattice areas. After a brief introduction in which we discuss the reasons that finite density QCD is an active and important subject, we present the fundamental formulae that are necessary for the treatment given in the following sections. Next, we survey lattice QCD simulational studies of system with small chemical potentials, of which there have been several prominent works reported recently. Then, two-color QCD calculations are discussed, where we are free from the notorious phase problem and have a chance to consider many new features of finite density QCD. Of special note is the result of recent simulations indicating quark pair condensation and the in-medium effect. Tables of SU(3) and SU(2) lattice simulations at finite baryon density are given. In the next section, we survey several related works that may represent a starting point of future development, although some of these works have not attracted much attention yet. This material is described in a pedagogical manner. Starting from a simple 2-d model, we briefly discuss a lattice analysis of the NJL model. We describe a non-perturbative analytic approach, i.e., the strong coupling approximation method and some results. The canonical ensemble approach, instead of the usual grand canonical ensemble may be another route to reach high density. We examine the density of state method and show that this old idea includes the recently proposed factorization method. An alternative method, the complex Langevin equation, and an interesting model, the finite isospin model, are also discussed. We give brief comments on a partial sum with respect to Z3 symmetry and the meron-cluster algorithm, which might solve the sign problem partially or completely. In the Appendix, we discuss several technical points that are useful in practical calculations.

Chiho Nonaka

Papers

Hadronization in Heavy-Ion Collisions: Recombination and Fragmentation of Partons

Hadron production in heavy ion collisions: Fragmentation and recombination from a dense parton phase

Space-time evolution of bulk QCD matter

Systematic comparison of jet energy-loss schemes in a realistic hydrodynamic medium

Lattice QCD at Finite Density An Introductory Review