Fusing the vector bosons: Higgs Production Through VBF and WW Scattering at the Current and Future LHC

A long search for the Higgs boson was successfully concluded in the summer of 2012. Ever since, efforts are put into precisely measuring all its properties, its production and decay rates, to verify if this is indeed the particle predicted by the Standard Model (SM) or a first evidence of some New Physics. This thesis describes the search for a specific combination of the Higgs boson production and decay modes which have not been observed so far - the Vector Boson Fusion (VBF) production with the Higgs boson decaying into a pair of W bosons. After the introduction, this thesis is divided into two parts: ‘the first run at the LHC’ and ‘the future runs at the LHC’. The first part describes the theoretical overview of the SM and the Higgs boson in chapters 1 and 2, respectively, followed by the description of the LHC and the ATLAS detector in chapter 3, event and object reconstruction in chapter 4 and the VBF H -> WW analysis in chapters 5 through 7. One of the focuses of this thesis is the treatment of systematic uncertainties of one of the largest backgrounds in the VBF H->WW analysis, the top-quark decays, and is presented in chapter 6. The second part of this thesis starts by describing the scheduled upgrades of the LHC and the ATLAS detector in chapter 8. Chapters 9 and 10 are dedicated to two different feasibility studies; the first one analyses the benefits future LHC runs may bring to the VBF H->WW measurement and the second one studies the impact of the future ATLAS detector on the significance measurement of vector boson scattering (another processes which allows us to study the nature of the Higgs boson) and the sensitivity for New Physics. The thesis finishes with the conclusion and summary.