Investigation of Quark Gluon Plasma-like signals with Lund string interactions

Abstract: This thesis investigates the interactions that occur in extreme densities for high-energy collisions of subatomic particles. The theoretical models developed for this purpose are based on the Lund model. The developments have been implemented as a new module called Gleipnir to the Monte-Carlo event generator, P YTHIA . The two models developed are string shoving and rope hadronization, and can now be used for proton-proton, proton-nucleus and nucleus-nucleus collisions.Paper I presents a novel method to calculate string shoving in all systems. The strings are considered as colour flux-tubes, with colour electric fields with transverse extent. The force between two colour flux tubes is calculated in a special Lorentz frame called the parallel frame. Final state collectivity reproduced by string shoving is investigated in both small and large systems. We conclude that further modifications to string shoving are required to be able to produce a better agreement with experimental data for large systems.Paper II presents the rope hadronization mechanism using the parallel frame. Rope hadronization would modify the strangeness yields, and this effect can be observed in jets as well. The system of interest is jet-triggered proton-proton collisions, where we probe the yields of strange hadrons and baryons in a jet. We find significant enhance-ment of strangeness, particularly strange baryons in the jet.Paper III shows the enhancement in strangeness yields with rope hadronization in all systems, using the tech-niques introduced in Paper I and Paper II. The formalism produces significant improvements over default Pythia and Angantyr. To be able to reproduce a better agreement to data, further modifications are necessary, such as the inclusion of string shoving mechanism.Paper IV describes the correction to production vertices of primary hadrons from string interactions for both small and large systems. The impact from string shoving is found to be higher than compared to rope hadronization. This would influence other P YTHIA processes that build on primary hadronic vertices such as hadronic rescattering.