Perturbative QCD in event generation

Abstract

This thesis is concerned with the simulation of particle physics processes involving strong interactions in modern event generators. New algorithms to reinstate colour in colour- ordered amplitudes through colour dressing are presented and their analytical and numerical properties are discussed in detail. The colour-dressed Berends-Giele recursive relations are extended to the full Standard Model Lagrangian and implemented into the numerical program Comix for large multiplicity matrix element computation. New algorithms for phase space integration are proposed, whereof one is capable to effectively couple colour and momentum sampling. Comparisons to other high-multiplicity generators are shown. QCD parton evolution and the CKKW algorithm to correctly include real next-to-leading order corrections are revisited. New types of jet measures are proposed for the merging of matrix elements and parton showers and their analytical and numerical properties are discussed. The implementation into the event generator Sherpa is presented using two different types of matrix element generators. Corresponding results and comparisons are shown. A further comparison between different types of merging algorithms is presented, including various numerical codes, which implement different merging approaches. Finally, the implementation of BFKL evolution in a Markovian approach is introduced and corresponding results from a numerical simulation are presented. Implications on event generation for current and future colliders are discussed throughout.