On the Energy Dependence of Parameters in PYTHIA8 Heavy-ion Collision Simulations

Abstract: Particle collisions are an essential component to the research methodology of particle physics. These investigations are not only conducted in experimental laboratories but also through programs such as PYTHIA that simulate a collision or ``event" and then compare its results to known experimental data. This thesis aims to investigate the energy dependence of parameters used in PYTHIA's Angantyr model for heavy-ion collisions. A significant portion of this project was dedicated to collecting the output of simulated collisions within the energy range of 10 GeV - 10 TeV. The focus was mainly on three parameters in the Angantyr model ($k_0$, $\alpha$, and $\sigma_D$) and their parametrizations with respect to the center of mass energy of the collision. This was performed for two versions of Angantyr that differ in the treatment of the opacity of the colliding particles. In the default version a larger particle radius leads to a more opaque particle, and in the second version a smaller radius implies a more opaque particle. It was found that the second version of Angantyr outperformed the default, especially in the low energy range. Additionally, once the functional forms of the relevant parameters of Angantyr were known, they were used to create a Parameterized Energy Dependence (PED) model. It had good agreement with experimental data and therefore the functional forms of the parameters are deemed useful for a possible implementation into PYTHIA.