Hadronic Interactions at High and Low Energies

Abstract: In the past, development of the PYTHIA event generator has mainly concentrated on the physics of proton–proton collisions at high energies, as this is the most important case to modern high energy physics experiments. However, there are situations where more generic beam configurations are relevant. This thesis presents implementations and applications of such processes in PYTHIA. The two applications discussed in this thesis are hadronic rescattering, and hadronic cascades in media. These are developed in Papers I and Iv, while Papers II and III present physics studies of rescattering.Paper I: A framework for hadronic rescattering is implemented. This includes both the rescattering algorithm itself, as well as modelling low energy interactions. Model tests are presented for proton–proton collisions.Paper II: The effects of rescattering in heavy ion collisions are studied, using the ANGANTYR framework to simulate the collisions. Of note, results indicate that rescattering can produce a significant amount of collective flow.Paper III: This work studies rescattering as a production mechanism for exotic hadrons, specifically the $χ_{c1}(3872)$ tetraquark and the $P_c^+(4312)$, $P_c^+(4440)$ and $P_c^+(4457)$ pentaquarks.Paper IV: Modelling of high energy collisions in PYTHIA is extended to general hadron–nucleon interactions. The major parts of this extension are to define cross sections for these interactions and parton distribution functions for the hadrons involved. The paper studies the features of this model in the context of hadronic cascades in media, primarily cascades initiated by cosmic rays in the atmosphere, using a toy model.