Centrality dependence of particle yields and their ratios at RHIC experiments
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I, PARTICLES, FIELDS, GRAVITATION, AND ASTROPHYSICS
Centrality Dependence of Particle Yields and Their Ratios at RHIC Experiments Inam-ul Bashir Department of Physics, Islamic University of Science and Technology, Pulwama, Kashmir, India e-mail: [email protected] Received July 29, 2016
Abstract—The collision centrality dependence of the yields per unit rapidity dN/dy along with their ratios for various hadrons produced in Au+Au collisions at different collision energies have been studied within the framework of unified statistical thermal freeze-out model (USTFM) taking into account both longitudinal and transverse hydrodynamic flows. Bulk freeze-out properties in terms of the thermal parameters, temperature and mid-rapidity baryon chemical potential at chemical freeze-out, obtained within the proposed model, which are in agreement with experimental data. The extracted chemical freeze-out temperature is found to depend weakly on the collision centrality. It is also found that this temperature is almost independent of the collision energies considered in this work. The closeness of the freeze-out temperature to the predicted phase-transition temperature suggests that the chemical freeze-out happens near hadronization. Furthermore, the dependence of the mid-rapidity chemical potential on the collision energy at different centralities, as well as the centrality dependence of the mid-rapidity size of the system in terms of the transverse size of the system, has been studied at the RHIC. The effect of resonance decay contributions has also been taken into account. DOI: 10.1134/S1063776117070160
1. INTRODUCTION
ion collisions [6]. The statistical (thermal) models successfully describe the ratios of hadron yields in heavy ion collisions. The agreement of the particle yield ratios with simple predictions of the statistical models is a key reason for the thermalization of the system formed in heavy-ion collisions. Measurements of antiparticle-to-particle yield ratios in these collisions give information on the net baryon density or the baryon chemical potential. Thus, these measurements are of interest in characterizing the environment created in these collisions. It was also suggested that the measurement of strange antibaryon-to-baryon yield ratios could help distinguish between a hadron gas and a deconfined quark–gluon plasma [7]. For a boostinvariant system at mid-rapidity for the RHIC and LHC energies, the particle yields dN/dy change only by a few percent in the rapidity range |y| < 1. Although the particles detected at mid-rapidity are collected from various parts of a fireball, their yield ratios are the same as in the 4π calculations. This holds even when the resonance decays are taken into account. In this work, the phenomenological boost-invariant unified statistical thermal freeze-out model (USTFM) [8] is employed. In this model, all hadrons in the hadron gas resulting from high-energy nuclear collisions at freeze-out have an equilibrium distribution. The local particle densities in the phase space have the fo
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