Colour Reconnection and Weak Showers

Sammanfattning: This thesis consider the improvement of the simulation tools used to describe high energy particle collisions. These simulation programs are normally referred to as event generators. The emphasis is on two specific parts of the event generation: the introduction of radiation of weak bosons associated with the collision and a new model for colour reconnection. Each collision contains significant additional radiation of particles, but earlier models have only included QCD and QED radiation. This thesis presents a first attempt at including also the weak radiation. The inclusion of weak emissions allows for a better understanding of already observed data. The weak radiation is also included in the common framework for including multi-jet matrix elements into the description of the radiation. Colour Reconnection (CR) address the question: between which partons do colour strings form? The new model incorporates three principles, the SU(3) colour rules from QCD, a space-time causality requirement, and a minimization of the potential energy. It also introduces a new type of reconnections producing junction structures. The new model is able to explain the lambda production simultaneously at both LEP and LHC. The effects of CR, both the new model as well as older models, are also considered at potential future electron-positron colliders. Comparisons between the new model and a string rope model is carried out, which include suggestions for relevant observables.