[Paper Review] Hadron production in Pb-Pb collisions at 158A GeV

Johann Rafelski, Jean Letessier|ArXiv.org|Mar 8, 1999

High-Energy Particle Collisions Research3 citations

TL;DR

This paper applies a Fermi statistical model to hadron production data from Pb-Pb collisions at 158 A GeV, analyzing particle abundances and spectra to infer properties of a transient quark-gluon plasma. It finds a freeze-out temperature of T_f ≈ 140–150 MeV and a baryochemical potential μ_B ≈ 200–210 MeV, significantly lower than prior expectations, consistent with a hadronizing, deconfined fireball phase.

ABSTRACT

A Fermi statistical model analysis of hadron abundances and spectra obtained in several relativistic heavy ion collision experiments is utilized to characterize a particle source. Properties consistent with a disintegrating, hadron evaporating, deconfined quark-gluon plasma phase fireball are obtained, with a baryochemical potential μ_B=200-210MeV, and a temperature T_f\simeq 140-150MeV, significantly below previous expectations.

Motivation & Objective

• To characterize the particle source produced in Pb-Pb collisions at 158 A GeV using hadron abundance and spectral data.
• To test whether the observed particle yields and spectra are consistent with a thermalized, hadronizing quark-gluon plasma phase.
• To determine the freeze-out temperature and baryochemical potential of the system, challenging previous estimates.
• To assess constraints from pion condensation on the extracted thermodynamic parameters.

Proposed method

• A Fermi statistical model is applied to describe the hadron abundances and momentum spectra measured in relativistic heavy ion collisions.
• The model assumes thermal equilibrium at freeze-out, with parameters T_f (freeze-out temperature) and μ_B (baryochemical potential) extracted from fitting experimental data.
• Particle yields are calculated using the grand canonical ensemble with conservation of baryon number, strangeness, and electric charge.
• The model incorporates relativistic kinematics and Fermi-Dirac statistics for baryons and Bose-Einstein statistics for mesons.
• Constraints from pion condensation are evaluated to rule out unphysical parameter regions.
• The analysis uses data from multiple experiments, including NA49 and NA50, to validate the extracted parameters.

Experimental results

Research questions

• RQ1 What are the thermodynamic parameters (T_f and μ_B) characterizing the particle source in Pb-Pb collisions at 158 A GeV?
• RQ2 Is the observed hadron yield and spectrum consistent with a thermalized, deconfined quark-gluon plasma phase?
• RQ3 How do the extracted parameters compare to previous theoretical expectations?
• RQ4 What role does pion condensation play in constraining the allowed parameter space for T_f and μ_B?
• RQ5 Can the Fermi statistical model successfully describe both particle abundances and spectra simultaneously?

Key findings

• The freeze-out temperature is determined to be T_f ≈ 140–150 MeV, significantly lower than earlier estimates.
• The baryochemical potential is found to be μ_B ≈ 200–210 MeV, indicating a high baryon density in the system.
• The extracted parameters are consistent with a disintegrating, hadron-evaporating, deconfined quark-gluon plasma phase.
• The model fits both hadron abundances and spectra simultaneously, supporting the validity of the thermal description.
• Constraints from pion condensation are satisfied, reinforcing the physical consistency of the extracted parameters.
• The results challenge previous expectations of higher temperatures, suggesting a more moderate evolution of the fireball.