Search for a heavy Scalar Boson in the 2 Higgs Doublet Model with the ATLAS Detector

The analysis presented in this thesis shows a search for a heavy scalar boson in the 2-Higgs-doublet-model (2HDM) framework, carried out in the $h/H \rightarrow WW \rightarrow e \nu \mu \nu$ decay channel. Under the assumption, that the light Higgs boson of the 2HDM coincides with the particle discovered with a mass of 125 GeV, the search is performed in the $\cos(\beta-\alpha)$ vs. $m_H$ plane using 20.3 $\text{fb}^{-1}$ of collision data recorded by the ATLAS detector in 2012 with a centre-of-mass energy of 8 TeV. Since no evidence for an additional heavy Higgs boson H can be found in the investigated mass range of 135 GeV to 1000 GeV, excluded phase space regions with 95% CL are given for Type-I and Type-II 2HDMs for different values of $\tan(\beta)$. In both models, large parts of the parameter space can be excluded for masses up to 1000 GeV.