Abstract
Within the first few microseconds from after the Big Bang, the hot dense matter was in the form of the Quark Gluon Plasm (QGP) consisting of free quarks and gluons. By colliding heavy nuclei at RHIC and LHC at a velocity close to the speed of light, we were able to create the primordial matter and observe the matter after expansion and cooling. In this report we present the thermodynamics and transport coefficients obtained in the framework of clustering of color sources in both hadron-hadron and nucleus-nucleus collisions at RHIC and LHC energies. Multiparticle production at high energies can be described in terms of color strings stretched between the projectile and target. At high string density single strings overlap and form color sources. This addition belongs to the non-perturbative domain of Quantum Chromo Dynamics (QGP) and manifests its most fundamental features. The Schwinger QED 2 mechanism produces color neutral q q ¯ pairs when color source strings break. Subsequent hardonization produces the observed hadrons. With growing energy and atomic number of the colliding nuclei the density of strings grows and more color sources form clusters in the transverse plane. At a certain critical density a macroscopic cluster appears, which marks the percolation phase transition. This is the Color String Percolation Model (CSPM). The critical density is identified as the deconfinement transition and happens at the hadronization temperature. The stochastic thermalization in p p and A-A is a consequence of the quantum tunneling through the event horizon introduced by the confining color fields, the Hawking-Unruh effect. The percolation approach within CSPM is successfully used to describe the crossover phase transition in the soft collision region. The same phenomenology when applied to both hadron-hadron and nucleus-nucleus collisions emphasizes the importance of color string density, creating a macroscopic cluster which identifies the connectivity required for a finite droplet of the QGP.
Highlights
What is the behavior of matter when we increase its density? The observed densities of our world expand over many orders of magnitude, from ∼10−6 nucleons/cm3 on average in our universe to ∼1038 nucleons/cm3 inside a nucleus and 1039 nucleons/cm3 in a neutron star
The same phenomenology when applied to both hadron-hadron and nucleus-nucleus collisions emphasizes the importance of color string density, creating a macroscopic cluster which identifies the connectivity required for a finite droplet of the Quark Gluon Plasm (QGP)
The study of the high density limit, the confinement transition from hadrons to quarks and gluons can be regarded as the place where a high energy collision probes the short range limit and meets the thermodynamics of this short distance dynamics
Summary
What is the behavior of matter when we increase its density? The observed densities of our world expand over many orders of magnitude, from ∼10−6 nucleons/cm on average in our universe to ∼1038 nucleons/cm inside a nucleus and 1039 nucleons/cm in a neutron star. The study of the high density limit, the confinement transition from hadrons to quarks and gluons can be regarded as the place where a high energy collision (two body) probes the short range limit and meets the thermodynamics (many body) of this short distance dynamics. The lattice QCD studies have shown, that at baryon chemical density μ B ∼ 0, color deconfinement and chiral symmetry restoration coincide. In a medium of low baryon density, the mass of the constituent quark vanishes at the deconfinement point Tc and the screening radius of the gluon cloud size vanishes. At low T and high μ, there is no reason to expect a similar behavior and probably there may be an intermediate region of massive dressed quarks between the hadronic phase and the deconfined and chiral symmetry restoration phase. There are other review articles in the literature on the deconfinement both in pp and AA collisions [5,6,7]
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