ALPACA - A kinetic theory Monte Carlo event generator for heavy ion collisions

Sammanfattning: Recent measurements of collective effect-like signals in small collision systems has highlighted the need for new models to explain these phenomena. One good candidate for such a model is the AMY QCD effective kinetic theory, which is valid for systems in- and out-of-equilibrium. This thesis is a collection of four papers which all investigate how to apply AMY kinetic theory to explain the evolution of small and large collision systems. In Paper I an analytical approach is used to extract collective flow coefficients from the kinetic theory. Paper II-IV then show the main work of the thesis, an implementation of the kinetic theory in the form of an event generator called ALPACA, as well as applications of this event generator to different systems.Paper I presents results derived from the single-hit approximation of AMY kinetic theory looking specifically at the energy flow response to initial geometrical deformations in a purely gluonic system. It results in a scaling formula for the collective flow coefficients, and a proof-of-concept study of the flow response for small collision systems, which gives results that are correct in order of magnitude.Paper II presents the main work of the thesis, the Monte Carlo event generator ALPACA (AMY Lorentz invariant PArton CAscade). The details of how the event generator is implemented to faithfully reproduce the dynamics of AMY kinetic theory are discussed, and a validation of the framework in the case of an infinite thermal equilibrium is shown.Paper III show how different systems thermalize and isotropize in ALPACA. Two different scenarios are analyzed; an overoccupied thermal system for thermalization, and isoptropization for anisoptropic Color Glass Condensate-like initial conditions. It is found that the system thermalizes correctly for the overoccupied case, compared to known analytical results.Paper IV investigates collective flow in small systems using Color Glass Condensate-like initial conditions in ALPACA. Comparisons between the single-hit approach of Paper I and ALPACA are made, and the details of the difference between first-hit, single-hit and all-hit are shown and discussed.