Parton Shower Algorithms - Possible Improvements
Abstract: In this Master thesis, two directions have been explored to improve the current parton shower algorithm of the event generator Pythia. Firstly, three choices of transverse-momentum-ordered evolution variable have been studied for final-state radiation in order to allow more flexibility within the algorithm. These three choices turn out to be valid but they lead to more technical implementations than the default evolution variable. Secondly, a new approach, involving colour dipoles, has been set up to deal locally with recoils in initial-state radiation. It is a complementary procedure to the one present in the current version of Pythia, which is based on global recoils. This new procedure has been implemented and compared to the default one through some simulations. The use of the dipole framework leads to a smooth combination of initial-state radiation and final-state radiation. Some specific cases, such as deep inelastic scattering, are better described with this new approach. The matching between Feynman graphs and parton shower also benefits from this framework.
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