Freeze-Out Parameters in Heavy-Ion Collisions at AGS, SPS, RHIC, and LHC Energies

Sandeep Chatterjee,Sabita Das,Natasha Sharma,Lokesh Kumar,Bedangadas Mohanty,Raghunath Sahoo,D. Mishra

doi:10.1155/2015/349013

Abstract

We review the chemical and kinetic freeze-out conditions in high energy heavy-ion collisions for AGS, SPS, RHIC, and LHC energies. Chemical freeze-out parameters are obtained using produced particle yields in central collisions while the corresponding kinetic freeze-out parameters are obtained using transverse momentum distributions of produced particles. For chemical freeze-out, different freeze-out scenarios are discussed such as single and double/flavor dependent freeze-out surfaces. Kinetic freeze-out parameters are obtained by doing hydrodynamic inspired blast wave fit to the transverse momentum distributions. The beam energy and centrality dependence of transverse energy per charged particle multiplicity are studied to address the constant energy per particle freeze-out criteria in heavy-ion collisions.

Highlights

As a result of ultrarelativistic collision between two heavy ions, a fireball is expected to form that rapidly thermalizes
Since scattering could be both elastic and inelastic, it is possible to have two distinct freeze-outs, namely, chemical freeze-out (CFO), where inelastic collisions cease, and thermal/kinetic freeze-out (KFO) where elastic collisions cease and the particle mean free path becomes higher than the system size, which forbids the elastic collision of the constituents in the system [1]
In addition to the AGS [28,29,30,31,32,33,34,35,36,37], SPS [38,39,40,41,42,43,44,45,46], RHIC data at √sNN = 62.4, 130, and 200 GeV [55,56,57,58,59,60,61,62], and LHC [63] for which the CFO thermal parameters within 1CFO have been already well established, here we have analysed the preliminary data from RHIC Beam Energy Scan (BES) program [47, 73,74,75,76,77,78] at √sNN = 7.7, 11.5, 19.6, 27, and 39 GeV [48,49,50,51,52,53,54]

Summary

Introduction

As a result of ultrarelativistic collision between two heavy ions, a fireball is expected to form that rapidly thermalizes. The enormous amount of energy density deposited in the fireball results in large pressure gradients from the central to the peripheral region of the fireball that drives the expansion of the fireball. This expansion leads to cooling of the fireball. Freezeout could be a complicated process involving duration in time and a hierarchy where different types of particles and reactions switch-off at different times. This leads to the concept of “sequential freeze-out.”.

Chemical Freeze-Out

Transverse Energy per Charged Particle and Freeze-Out Criteria

Kinetic Freeze-Out

Summary