Optimization of the Reconstruction of the Missing Transversal Momentum the new Software of the ATLAS Experiment

Many of the processes described and hence predicted by the Standard Model of particle physics were already observed and verify that theory in this way. Some vector boson scattering processes belong to the predictions which have not been measured precisely so far. It is the aim of current efforts to use the data from the ATLAS experiment at the LHC (CERN) to succed with the verification. Commonly appearing decay products of $W^{\pm}$bosons involved in such scattering processes are neutrinos. These particles interact only very weakly and are therefore practically undetectable at the ATLAS experiment. To gain information about them anyhow, it is necessary to use an indirect method. The consideration of the missing transversal momentum (MET) seems to be constructive because it can be directly associated with the transversal energy of the neutrino. The MET reconstruction based on the given detector signals is performed with the ATLAS software Athena which was recently updated to version 21. That new version adds several variations of the reconstruction algorithm to the existing ones, for example by defining and calibrating new working points for the jet selection. This bachelor thesis is targeted on the investigation of the available variations in order to find the most appropriate ones for the application in the research on vector boson scattering. Therefore, the algorithm is applied to data samples from Monte Carlo simulations of the process $W^{\pm} Z \rightarrow W^{\pm} Z$. By comparing the obtained results with the truth values, the MET reconstruction performance is evaluated and conclusions are made about the differences between the variations.