Extracting Speed Of Sound Parameter From Heavy-Ion Collisions At High Energies

High energy heavy-ion (nucleus-nucleus) collisions are an important research topic in fields of particle and nuclear physics. Many charged and neutral particles are produced in the collisions. By studying the rapidity (pseudorapidity) distributions of final-state particles, we can understand the production processes of particles in the interacting system. Many theoretical models have been introduced to describe the particle productions. Among the theoretical models, Landau hydrodynamic model is one of the most useful treatment methods in high energy heavy-ion collisions.Presently, the Landau hydrodynamic model works well from the Alternating Gradient Synchrotron (AGS) to the Relativistic Heavy Ion Collider (RHIC) energies. The Landau hydrodynamic model is successfully applied to investigate the pseudorapidity distribution dNch/dη and its dependences on center-of-mass energy, collision centrality, and sizes of target or projectile nuclei at RHIC energies. We noticed that the characteristics of pseudorapidity distributions at LHC energies are similar to those at RHIC energies. Thus, the Landau hydrodynamic model should be applied in heavy-ion collisions at LHC energies.In this thesis, the first issue finished by the author is the revision and improvement of the Landau hydrodynamic model. The projectile/target participants and the projectile/target spectators are respectively described by the model at RHIC and LHC energies. The pseudorapidity distributions of final-state charged particles produced in Au+Au and Cu+Cu collisions with different centralities at RHIC energies and those in Pb+Pb collisions with different centralities at LHC energies are analyzed and found to be in good agreement with experimental data. The Landau hydrodynamic model is then applied in a wider energy range.In high energy heavy-ion collisions, the square speed of sound, cs2, is a quantity which cannot be measured directly in experiments. However, the measurement of speed of sound is very important in high energy collisions. The second issue finished by the author in this thesis is the proposal of an effective method measuring the speed of sound. This method is only based on the width of pseudorapidity distributions and can be easily used in practice. It is shown that the speeds of sound for the projectile/target participants and for the projectile/target spectators are consistent each other in the statistical errors. Meanwhile, the obtained results are in agreement with the hadron resonance gas (HRG) model and the lattice quantum chromodynamics (QCD) theory.