Multiplicity and Pseudorapidity Distributions of relativistic charged particles in Pb-Pb Collisions at 158A GeV/c

Introduction One of the main goals to study the characteristics of multiparticle production in relativistic heavy-ion collisions is to understand the underlying dynamics involved in phasetransition of produced nuclear matter into final state hadrons. A further impetus to these studies has emerged after the promising chance of quark-gluon plasma (QGP) formation has emerged at RHIC and LHC. Under the conditions of extreme density and temperature; the heavy nuclei collisions at high enough energy serve as a unique tool to study the strongly interacting matter. The fluctuations in hadron multiplicity produced in heavy-ion collisions may provide some clues for the occurrence of phase-transition [1]. At relativistic high energies, nucleons of the colliding nuclei deposit a huge amount of energy in a very small region of space resulting in the very high energy density (of the order GeV/fm) for a very short duration of time [2]. The final state particles produced from the spacetime evolution of such collisions carry important information about the mechanism of particle production. To analyze these type of collision processes, the investigation of charged secondary particles play a significant role [3]. In the experiments where nuclear emulsion is used, a special preference is given to singly charged particles having velocity more than 70 percent of the light velocity. The shower particles are such singly charged particles with the relative speed, β≥0.7. These particles are mostly the relativistic charged pions with a few kaons and protons. The ionization on the tracks of these particles is g < 1.4go; where go is the minimum ionization on the tracks of singly charged particles. It has been found more suitable to study the properties of only shower particles than an admixture of all the charged particles; because such an admixture also contains fragments from both the nuclei having totally different mass, energy and centrality dependence. Furthermore, the multiplicity of shower particles (NS) is shown directly to be a parameter of the number of nucleons involved. The pseudorapidity distribution can be obtained directly in the relativistic heavy-ion interactions. Thus it provides a viable method to study the process and mechanism of particle production. The emission angle (θ) for shower particles can be measured precisely, and it is usually presented in the terms of pseudorapidity variable η= -ln tan(θ/2). Pseudorapidity variable is considered as one of the vital kinematical variables and its distribution is very helpful in yielding the information related to the multiparticle production mechanism.