Particle ratios and the QCD critical temperature (original) (raw)

Hagedorn States and Thermalization in Heavy Ion Collisions

2011

In recent years, Hagedorn states have been used to explain the equilibrium and transport properties of a hadron gas close to the QCD critical temperature. These massive resonances are shown to lower η/s to near the AdS/CFT limit close to the phase transition. A comparison of the Hagedorn model to recent lattice results is made and it is found that the hadrons can reach chemical equilibrium almost immediately, well before the chemical freeze-out temperatures found in thermal fits for a hadron gas without Hagedorn states.

Equilibrium Statistical-Thermal Models in High-Energy Physics

We review some recent highlights from the applications of statistical-thermal models to different experimental measurements and lattice QCD thermodynamics, that have been made during the last decade. We start with a short review of the historical milestones on the path of constructing statistical-thermal models for heavy-ion physics. We discovered that Heinz Koppe formulated in 1948 an almost complete recipe for the statistical-thermal models. In 1950, Enrico Fermi generalized this statistical approach, in which he started with a general cross-section formula and inserted into it simplifying assumptions about the matrix element of the interaction process that likely reflects many features of the high-energy reactions dominated by density in the phase space of final states. In 1964, Hagedorn systematically analysed the high-energy phenomena using all tools of statistical physics and introduced the concept of limiting temperature based on the statistical bootstrap model. It turns to be quite often that many-particle systems can be studied with the help of statistical-thermal methods. The analysis of yield multiplicities in high-energy collisions gives an overwhelming evidence for the chemical equilibrium in the final state. The strange particles might be an exception, as they are suppressed at lower beam energies. However, their relative yields fulfil statistical equilibrium, as well. We review the equilibrium statistical-thermal models for particle production, fluctuations and collective flow in heavy-ion experiments. We also review their reproduction of the lattice QCD thermodynamics at vanishing and finite chemical potential. During the last decade, five conditions have been suggested to describe the universal behavior of the chemical freeze out parameters. The higher order moments of multiplicity have been discussed. They offer deep insights about particle production and to critical fluctuations. Therefore, we use them to describe the freeze out parameters and suggest the location of the QCD critical endpoint. Various extensions have been proposed in order to take into consideration the possible deviations of the ideal hadron gas. We highlight various types of interactions, dissipative properties and location-dependences (spacial rapidity). Furthermore, we review three models combining hadronic with partonic phases; quasi-particle model, linear σ-model with Polyakov-loop potentials and compressible bag model.

Thermalization through Hagedorn states: the importance of multiparticle collisions

Journal of Physics G: Nuclear and Particle Physics, 2010

Quick chemical equilibration times of hadrons within a hadron gas are explained dynamically using Hagedorn states, which drive particles into equilibrium close to the critical temperature. Within this scheme master equations are employed for the chemical equilibration of various hadronic particles like (strange) baryon and antibaryons. A comparison of the Hagedorn model to recent lattice results is made and it is found that for both Tc =176 MeV and Tc=196 MeV, the hadrons can reach chemical equilibrium almost immediately, well before the chemical freeze-out temperatures found in thermal fits for a hadron gas without Hagedorn states. ‡

Particle ratios from AGS to RHIC in an interacting hadronic model

Journal of Physics G: Nuclear and Particle Physics, 2004

The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU (3) σ -ω approach. The commonly adopted non-interacting gas calculations yield temperatures close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. In contrast, the chiral SU (3) model predicts temperature and density dependent effective hadron masses and effective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three different parametrizations of the model, which show different types of phase transition behaviour, are investigated. We show that if a chiral phase transition occured in those collisions, 'freezing' of the relative hadron abundances in the symmetric phase is excluded by the data. Therefore, either very rapid chemical equilibration must occur in the broken phase, or the measured hadron ratios are the outcome of the dynamical symmetry breaking. Furthermore, the extracted chemical freeze-out parameters differ considerably from those obtained in simple non-interacting gas calculations. In particular, the three models yield up to 35 MeV lower temperatures than the free gas approximation. The inmedium masses turn out to differ up to 150 MeV from their vacuum values.

Particle ratios at RHIC: Effective hadron masses and chemical freeze-out

Physics Letters B, 2002

The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU (3) σ−ω approach. The commonly adopted noninteracting gas calculations yield temperatures close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. Contrary, the chiral SU (3) model predicts temperature and density dependent effective hadron masses and effective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three different parametrizations of the model, which show different types of phase transition behaviour, are investigated. We show that if a chiral phase transition occured in those collisions, "freezing" of the relative hadron abundances in the symmetric phase is excluded by the data. Therefore, either very rapid chemical equilibration must occur in the broken phase, or the measured hadron ratios are the outcome of the dynamical symmetry breaking. Furthermore, the extracted chemical freeze-out parameters differ considerably from those obtained in simple noninteracting gas calculations. In particular, the three models yield up to 35 MeV lower temperatures than the free gas approximation. The in-medium masses turn out differ up to 150 MeV from their vacuum values.

Hagedorn States and Thermalization

2011

Hadronization conditions in relativistic nuclear collisions and the QCD pseudo-critical line

Physics Letters B, 2017

We compare the reconstructed hadronization conditions in relativistic nuclear collisions in the nucleon-nucleon centre-of-mass energy range 4.7-2760 GeV in terms of temperature and baryonchemical potential with lattice QCD calculations, by using hadronic multiplicities. We obtain hadronization temperatures and baryon chemical potentials with a fit to measured multiplicities by correcting for the effect of post-hadronization rescattering. The post-hadronization modification factors are calculated by means of a coupled hydrodynamical-transport model simulation under the same conditions of approximate isothermal and isochemical decoupling as assumed in the statistical hadronization model fits to the data. The fit quality is considerably better than without rescattering corrections, as already found in previous work. The curvature of the obtained "true" hadronization pseudo-critical line κ is found to be 0.0048 ± 0.0026, in agreement with lattice QCD estimates; the pseudo-critical temperature at vanishing µB is found to be 164.3 ± 1.8 MeV.

Particle ratios and the QCD critical temperature (original) (raw)

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