Excluded volume hadron gas model for particle number ratios in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">A</mml:mi><mml:mo>+</mml:mo><mml:mi mathvariant="italic">A</mml:mi></mml:math>collisions

Yen, G.D.; Gorenstein, M. I.; Greiner, Walter; Yang, Shin Nan

doi:10.1103/physrevc.56.2210

Cited by 187 publications

(207 citation statements)

References 16 publications

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“…In fact, the total particle densities predicted by the thermal model, with parameters extracted from fits to experimental data, far exceed reasonable estimates and measurements based on yields and the system size inferred by pion interferometry [54]. It becomes necessary to take into account the Van der Waals-type excluded volume procedure [54,55,56].…”

Section: Excluded Volume Corrections (Grand-canonical Ensemble)mentioning

confidence: 99%

THERMUS—A thermal model package for ROOT

Wheaton

Cleymans

Hauer

2009

Computer Physics Communications

307

289

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THERMUS is a package of C++ classes and functions allowing statistical-thermal model analyses of particle production in relativistic heavy-ion collisions to be performed within the ROOT framework of analysis. Calculations are possible within three statistical ensembles; a grand-canonical treatment of the conserved charges B, S and Q, a fully canonical treatment of the conserved charges, and a mixedcanonical ensemble combining a canonical treatment of strangeness with a grandcanonical treatment of baryon number and electric charge. THERMUS allows for the assignment of decay chains and detector efficiencies specific to each particle yield, which enables sensible fitting of model parameters to experimental data. Nature of problem:Statistical-thermal model analyses of heavy-ion collision data require the calculation of both primordial particle densities and contributions from resonance decay. A set of thermal parameters (the number depending on the particular model imposed) and a set of thermalised particles, with their decays specified, is required as input to these models. The output is then a complete set of primordial thermal quantities for each particle, together with the contributions to the final particle yields from resonance decay.In many applications of statistical-thermal models it is required to fit experimental particle multiplicities or particle ratios. In such analyses, the input is a set of experimental yields and ratios, a set of particles comprising the assumed hadron resonance gas formed in the collision and the constraints to be placed on the system. The thermal model parameters consistent with the specified constraints leading to the best-fit to the experimental data are then output. Solution method:THERMUS is a package designed for incorporation into the ROOT [2] framework, used extensively by the heavy-ion community. As such, it utilises a great deal of ROOT's functionality in its operation. ROOT features used in THERMUS include its containers, the wrapper TMinuit implementing the MINUIT fitting package, and the TMath class of mathematical functions and routines. Arguably the most useful feature is the utilisation of CINT as the control language, which allows interactive 2 access to the THERMUS objects. Three distinct statistical ensembles are included in THERMUS, while additional options to include quantum statistics, resonance width and excluded volume corrections are also available. THERMUS provides a default particle list including all mesons (up to the K * 4 (2045)) and baryons (up to the Ω − ) listed in the July 2002 Particle Physics Booklet [3]. For each typically unstable particle in this list, THERMUS includes a text-file listing its decays. With thermal parameters specified, THERMUS calculates primordial thermal densities either by performing numerical integrations or else, in the case of the Boltzmann approximation without resonance width in the grand-canonical ensemble, by evaluating Bessel functions. Particle decay chains are then used to evaluate experimental observables...

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Section: Excluded Volume Corrections (Grand-canonical Ensemble)mentioning

confidence: 99%

THERMUS—A thermal model package for ROOT

Wheaton

Cleymans

Hauer

2009

Computer Physics Communications

307

289

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“…Then we compare and contrast it to what we refer to as model II [10], which appeared a decade later. Model II has been compared to experimental data a number of times, such as in [11] and [12]. Our arguments are phrased in terms of classical statistics, or Boltzmann distributions, for clarity of presentation.…”

Section: Excluded Volume Modelsmentioning

confidence: 99%

Matching excluded-volume hadron-resonance gas models and perturbative QCD to lattice calculations

2014

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We match three hadronic equations of state at low energy densities to a perturbatively computed equation of state of quarks and gluons at high energy densities. One of them includes all known hadrons treated as point particles, which approximates attractive interactions among hadrons. The other two include, in addition, repulsive interactions in the form of excluded volumes occupied by the hadrons. A switching function is employed to make the crossover transition from one phase to another without introducing a thermodynamic phase transition. A chi-square fit to accurate lattice calculations with temperature 100 < T < 1000 MeV determines the parameters. These parameters quantify the behavior of the QCD running gauge coupling and the hard core radius of protons and neutrons, which turns out to be 0.62 ± 0.04 fm. The most physically reasonable models include the excluded volume effect. Not only do they include the effects of attractive and repulsive interactions among hadrons, but they also achieve better agreement with lattice QCD calculations of the equation of state. The equations of state constructed in this paper do not result in a phase transition, at least not for the temperatures and baryon chemical potentials investigated. It remains to be seen how well these equations of state will represent experimental data on high energy heavy ion collisions when implemented in hydrodynamic simulations.

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“…The description of nuclear (as well as hadronic) collisions may be achieved in terms of semi-phenomenological models, which may be subdivided into macroscopic and microscopic models. Macroscopic models, like well-known hydrodynamic [1,2,3,4,5] or thermal [6,7,8,9] models use a few thermodynamic quantities like energy density, temperature, pressure, chemical potential, etc., to describe the macroscopic properties of a system of colliding nuclei. But the applicability of thermodynamics is based heavily on the hypothesis of local (or rather global) thermodynamical equilibrium (LTE) in the system.…”

Section: Introductionmentioning

confidence: 99%

Local thermal and chemical equilibration and the equation of state in relativistic heavy ion collisions

Bravina

Brandstetter

Gorenstein

et al. 1999

J. Phys. G: Nucl. Part. Phys.

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Abstract. Thermodynamical variables and their time evolution are studied for central relativistic heavy ion collisions from 10.7 to 160 AGeV in the microscopic Ultrarelativistic Quantum Molecular Dynamics model (UrQMD). The UrQMD model exhibits drastic deviations from equilibrium during the early high density phase of the collision. Local thermal and chemical equilibration of the hadronic matter seems to be established only at later stages of the quasi-isentropic expansion in the central reaction cell with volume 125 fm 3 . Baryon energy spectra in this cell are reproducedby Boltzmann distributions at all collision energies for t ≥10 fm/c with a unique rapidly dropping temperature. At these times the equation of state has a simple form: P ∼ = (0.12 − 0.15) ε. At SPS energies the strong deviation from chemical equilibrium is found for mesons, especially for pions, even at the late stage of the reaction. The final enhancement of pions is supported by experimental data.

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Excluded volume hadron gas model for particle number ratios inA+Acollisions

Cited by 187 publications

References 16 publications

THERMUS—A thermal model package for ROOT

THERMUS—A thermal model package for ROOT

Matching excluded-volume hadron-resonance gas models and perturbative QCD to lattice calculations

Local thermal and chemical equilibration and the equation of state in relativistic heavy ion collisions

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