High density matter at RHIC

QCD predicts a phase transition between hadronic matter and a quark-gluon plasma at high energy density. The relativistic heavy ion collider (RHIC) at Brookhaven National Laboratory is a new facility dedicated to the experimental study of matter under extreme conditions. Already the first round of experimental results at RHIC indicated that the conditions to create a new state of matter are indeed reached in the collisions of heavy nuclei. Studies of particle spectra and their correlations at low transverse momenta provide evidence of strong pressure gradients in the highly interacting dense medium and hint that we observe a system in thermal equilibrium. Recent runs with high statistics allow us to explore the regime of hard-scattering processes where the suppression of hadrons at large transverse momentum, and quenching of di-jets are observed thus providing further evidence for extreme high density matter created in collisions at RHIC.     

Space-time evolution of bulk QCD matter at RHIC

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 non-equilibrium model for the later hadronic stage where the equilibrium assumptions are not valid anymore. Within this approach we study the dynamics of hot, bulk QCD matter, which is being created in ultra-relativistic heavy-ion collisions at RHIC. In particular, we perform a detailed analysis of the reaction dynamics, hadronic freeze-out, transverse flow and elliptic flow. PACS 25.75.-q; 24.10.Nz; 24.10.Lx     

New forms of QCD matter discovered at RHIC

We discuss two special limiting forms of QCD matter which may be produced at RHIC. We conclude from the available empirical evidence that an equilibrated, but strongly coupled quark–gluon plasma has been made in such collisions. We also discuss the growing body of evidence that its source is a color glass condensate.     

The state of superdense matter

The equation of state of a superdense degenerate Fermi gas is investigated within an extended 7-dimensional phase space. The equation of states obtained and the sound velocity are analyzed, and the equilibrium configuration curve is given for superdense astronomic objects, taking into account the equation of state mentioned and threshold creation of baryons and their resonances within the given formalism.     

Symmetry breaking in superdense matter

A gauge theory for superdense matter is considered. It is shown that in the mean-field approximation at T = 0 °K the symmetry breaking increases with increasing density. The state of dense matter and the early Universe are shortly discussed.     

Latest results on the hot dense partonic matter at RHIC

At the Relativistic Heavy-Ion Collider (RHIC) collisions of heavy ions at nucleon-nucleon energies of 200GeV appear to have created a new form of matter thought to be a deconfined state of the partons that ordinarily are bound in nucleons. We discuss the evidence that a thermalized partonic medium, usually called a Quark Gluon Plasma (QGP), has been produced. Then, we discuss the effect of this high-density medium on the production of jets and their pair correlations. Next, we look at direct photons as a clean electro-magnetic probe to constrain the initial hard scatterings. Finally, we review the developing picture for the effect of this medium on the production of open heavy quarks and on the screening by the QGP of heavy-quark bound states.     

In-medium hadronization in the deconfined matter at RHIC and LHC

We study the mechanism and probability of in-medium hadronization in the deconfined medium produced in heavy-ion collisions at RHIC and LHC. We show the likelihood of color-neutral objects to be formed inside the partonic fireball and the probability of these states to escape the medium with reduced interaction strength and energy loss. We will suggest specific measurements that are sensitive to the early degrees of freedom and show predictions for these measurements at RHIC and the LHC.     

Equation of state of superdense matter

The possibility of the existence of anomalous nuclei in superdense stars as well as the possibility of the spontaneous transition of a superdense object as a whole into an anomalous state which can be due either to the Migdal or the Lee mechanisms are discussed. An equation of state is obtained for _Nucl by using data on the total proton-proton scattering cross section in the high-energy range.Translated from Izvestiya Vysshikh Uchbenykh Zavedenii, Fizika, No. 11, pp. 20–23, November, 1978.     

Non-equilibrium nuclear abundances in superdense matter

1. The equation of state and nuclear composition are calculated for cold matter below neutron-drip density (～4×10¹¹ g/cm³) using recent nuclear data. 2. Nuclear transmutations of hot and dense matter taking care of the freezing of nuclear reactions are discussed for three types of temperature and density changes.     

Exploring the phase diagram of strongly interacting matter; news from SPS and RHIC

Two experimental programs are aiming to study nuclear collisions in the energy regime in order to explore an essential part of the phase diagram of strongly interacting matter. The programs are motivated by observations that indicate a phase transition to take place in this energy domain: the onset of deconfinement. The STAR collaboration proposes an energy scan in the Relativistic Heavy Ion Collider (RHIC) at BNL. The ongoing program of the NA61/SHINE experiment consists of a two-dimensional energy-system size scan in nuclear and elementary collisions. The goal of both programs is to study the properties of the onset of deconfinement and to eventually discover the conjectured critical point of strongly interacting matter. A comparison of the strengths and limitations reveals the complementarity of the two programs.     

Quantum chromodynamics and the theory of superdense matter

At high enough density and/or temperature ordinary matter undergoes a transition into a plasma-like phase, consisting of quarks and gluons rather than of separate hadrons. Due to asymptotic freedom, the asymptotic properties of such matter can be calculated perturbatively, while in the discussion of phase transitions one should concentrate on nonperturbative effects. Recent progress in this theory is reviewed, as well as its applications to such topics as hadronic structure, neutron stars, high energy collisions of hadrons, etc.     

VISHNU hybrid model for the viscous QCD matter at RHIC and LHC energies

In this proceeding, we briefly describe the viscous hydrodynamics + hadron cascade hybrid model VISHNU for relativistic heavy ion collisions and report the current status on extracting the QGP viscosity from elliptic flow data.     

Exploring hybrid-star matter at NICA and FAIR

We discuss constraints for the equation of state of hybrid-star matter which can be obtained from next-generation heavy-ion collisions at FAIR and NICA. Particular emphasis is on the planned NICA facility at JINR (Dubna) which will provide fixed target and collider experiments just in the relevant energy ranges.     

Anisotropic flow at RHIC

STAR’s measurement of directed flow for pions,kaons（K 0 S ）,protons and anti-protons,for Au＋Au collisions at 200 GeV obtained in Run7 are presented,as well as elliptic flow for identified particles measured in Au＋Au（Run7） and Cu＋Cu（Run5） collisions.It is found that the slope of proton v 1 （y） at midrapidity is extremely small.Elliptic flow results are compared to Hydro calculation and the discrepancy is discussed.     

Heavy-ion collisions at RHIC

The European Physical Journal C - In the first three years of running, the four RHIC experiments have collected a rich set of high quality data on nuclear collisions over a wide range in collision...     

z Scaling at RHIC

The concept of z scaling reflecting the general regularities of high-p _T particle production is reviewed. Properties of data z presentation are discussed. New data on high-p _T particle spectra obtained at the RHIC are analyzed in the framework of z presentation. It was shown that these experimental data confirm z scaling. Predictions of strange particle spectra are considered to be useful for understanding of strangeness origin in mesons and baryons and search for new physics phenomena at the RHIC. The text was submitted by the author in English.     

Hydrodynamic flow at RHIC

We review the apparently hydrodynamic behaviour of low transverse momentum particles (pT ≤ 1.5 GeV/c) produced in central and semicentral (b ≤ 7 fm) heavy ion collisions at RHIC. We investigate the impact parameter dependence of various observables, elaborating on radial and elliptic flow and particle multiplicities. We also discuss possible ambiguities in the initialization of the hydrodynamic system and present observables that should allow for their resolution.     

Collective dynamics at RHIC

We discuss the strong collective flow effects, 〈v ₂〉 and 〈β _t 〉, observed at RHIC (√ ^s NN=130 GeV). We argue that part of the collectivity could have already developed at partonic stage. To ‘see’ the partonic effects directly, measurements of multi-strange baryons like Ξ, Ω and charmed particles like J/ψ transverse momentum distributions are important. They provide one of the possible keys to the discovery of collective modes with the partonic (quarks and gluons) degrees of freedom.