Measurement of Higgs boson production via gluon fusion and vector-boson fusion in the H $\to$ WW* decay mode with the ATLAS experiment at the LHC at $\sqrt{s}$ = 13 TeV

On the 4${}^{th}$ of July 2012 the observation of a new neutral particle was announced by the ATLAS [1] and CMS [2] Collaborations. This particle is by now generally considered as the Higgs boson H predicted [3,4] in the Standard Model of particle physics. Its mass of m${}_H$= 125.09±0.24 GeV [5] implies a rich set of final states which allow for experimental studies in regards to this particle and searches for deviations from the properties predicted by the Standard Model. In this thesis a measurement of the gluon-fusion and vector-boson fusion production cross sections times H $\to$ WW* branching ratio is presented using final states with one electron and one muon. The measurement is based on proton-proton collisions with an integrated luminosity of 36.1 fb${}^{\text{â}\text{ˆ}\text{’}1}$ recorded with the ATLAS detector at the CERN Large Hadron Collider (LHC) at $\sqrt{s}$ = 13 TeV in 2015 and 2016. Signal-like events are selected in categories with different jet multiplicities. The results are extracted by means of a binned maximum-likelihood fit. To this end, either distributions in multiple discriminant variables or the response of a multivariate classifier are used depending on the category. The results are found to be well compatible with the Standard Model predictions. This analysis is extrapolated to estimate the future precision of such a measurement at the end of the High-Luminosity LHC programme [6]. This extrapolated analysis is combined with analogously extrapolated analyses targeting other production and decay modes of the Higgs boson. Based on this combination the expected precision is determined for future measurements of couplings between the Higgs boson and other particles. Thereby an estimation is given for the anticipated sensitivity of these analyses to signs of physics beyond the Standard Model. In addition studies are presented to identify sources of electron charge misidentification in the reconstruction algorithms employed in the ATLAS Collaboration.