This thesis presents a study on how to reduce contamination of signals containing jets from so called pile-up jets. The Jet-Vertex-Tagger is used at the ATLAS detector to discriminate and between pile-up jets and the jets of interest originating from the hard scatter interaction, so called hard scatter jets. Several studies are presented on how to improve the Track-To-Vertex-Association of the Jet-Vertex-Tagger, where it is shown that substantial reduction of the pile-up contamination can be achieved by considering new selection criteria in the Track-To-Vertex-Association. Furthermore, the Jet-Vertex-Tagger is based on a likelihood which gives the relative probability for a jet to be hard scatter or pile-up.

In this thesis a study is presented which shows that an overall reduction of pile-up contamination can be accomplished by constructing a new likelihood based on a new jet definition called particle flow jets.
To measure di-Higgs production at the LHC is of great interest as it gives a direct possibility to measure the self-interaction of the Higgs boson. The self-interaction is of interest as it gives insight into the shape of the Higgs potential and the so called Electroweak Symmetry breaking. In this thesis a development of a method called reweighting is presented. The method enables interpretation of the Standard Model Effective Field Theory in the di-Higgs production channel known as gluon-gluon-Fusion.