Simulation and optimization studies for the measurement of the $t \bar{t} H(b \bar{b})$ process in the semileptonic channel at $\sqrt{s} = 13$ TeV with the ATLAS detector

The production of a Higgs boson in association with a top quark pair (ttH) allows a direct measurement of the Yukawa coupling of the top quark. This thesis consists of two studies with the aim of improving the measurement sensitivity and modelling accuracy in the detection of the ttH process in the ATLAS experiment. In an optimization study, several sets of configurations for the jet pT threshold are tested for sensitivity. Different configurations show robust behaviour and no improvement of the sensitivity can be ob- served compared to the ICHEP result in 2016. In a Monte Carlo generator study, the effect of the hdamp parameter in Powheg, and the renormalisation and factorisation scales in MadGraph, are investigated. The variation of the hdamp parameter has negligible effect on the events, while events produced with different generators and hadronisation models are found to show large deviations. The study on the renormalisation and factorisation scales shows that the different choices for the value of the scales in MadGraph and Powheg is one of the important origins of the deviation.