Tackling the Uncertainties of Event Generators

Abstract: This thesis is composed of four papers, which concern Monte Carlo event generators for high energy particle physics. Precise predictions of the outcome of particle collisions are important for the exploration of the Standard Model of particle physics at collider experiments like the LHC at CERN. The papers address the uncertainties of these predictions in different contexts.Paper I presents an algorithm for tuning Monte Carlo event generators with high dimensional parameter spaces by splitting the parameter space algorithmically. The algorithm is tested in ideal conditions and real-life examples of tuning Herwig and Pythia for LEP.Paper II concerns the perturbative uncertainty of unitarized next-to-leading order multi-jet merging prescriptions by discussing scale variations and scheme variations. The uncertainties are addressed for collisions at LEP and LHC.Paper III deals with QCD/QED interference effects in parton showers. For this purpose, we implement a shower including QED and QCD emissions and tree-level matrix element corrections for fixed color configurations.Paper IV proposes a method for the consistent removal of overlapping singularities in QCD parton showers at next-to-leading order in the strong coupling.