Semianalytical and Numerical Studies of Relativistic Heavy Ion Collisions

Abstract

The quark-gluon plasma (QGP) has been produced by relativistic heavy ion collisions, and understanding its properties is a primary goal in the field of nuclear physics. This research first elucidates recent semianalytical developments that improve the estimates of the initial energy and net conserved-charge densities and enable the calculation of trajectories in the quantum chromodynamics (QCD) phase diagram for the matter produced by nuclear collisions. A semianalytical model of the initial densities is developed by including the finite nuclear thickness for parton production. The new maximum energy density is found to have an analytical upper bound and satisfy an approximate scaling relation. QCD phase diagram trajectories are extracted from the semianalytical densities using several nuclear equations of state, and the calculated QGP lifetimes are found to depend significantly on the values of the model's parameters. The study next presents a comparison between two solutions of the relativistic Boltzmann equation (RBE): one, a numerical solution using parton trans- port; the other, a theoretical solution for a homogeneous gas of massless particles. Parton transport in Zhang's parton cascade (ZPC) is found to reproduce the results of a recent ex- act analytical solution of the RBE with an unexpected effectiveness at high densities when using new generalized collision schemes. Finally, the work discusses some open questions related to parton transport in ZPC and suggests some possible directions to uncover their answers. These future research goals include discovering the cause of an unexpected problem arising in simulations with three-dimensional (3D) expansion, understanding the theoretical distribution of the total center-of-mass (CM) energy squared for two-parton collisions, and studying curved parton motion in the presence of strong electromagnetic fields. Overall, the results presented in this dissertation improve the theoretical and numerical descriptions of the QGP and should be useful for future studies.