Search for Higgs bosons in Two-Higgs-Doublet models in the $H \rightarrow WW\rightarrow e \nu\mu\nu$ channel with the ATLAS detector

The Higgs-like boson observed at the LHC with a mass of approximately 125 GeV could be part of an extended scalar sector originating from two complex Higgs doublets. The analysis presented in this note investigates the possibility of a Two-Higgs-Doublet model (2HDM) being realized in nature by searching for evidence of a second, heavier, CP-even scalar boson in the $H\rightarrow WW^{(*)}\rightarrow e^{-} \bar{\nu} \, \mu^{+} \nu \, / \, e^{+} \nu \, \mu^{-} \bar{\nu}$ decay mode. The analysis is based on proton-proton collision data at a centre-of-mass energy of 8 TeV collected with the ATLAS detector and corresponding to an integrated luminosity of 13.0$\,\mathrm{fb^{-1}}$. Artificial neural network techniques are used to maximise the sensitivity. No evidence for a second scalar boson is found in the investigated mass range between 135 and 300 GeV. Exclusion limits on type-I and type-II 2HDMs are set as a function of the two mixing angles $\alpha$ and $\beta$ as well as the mass $m_H$ of the heavier scalar boson. For the limits the signal hypothesis includes the Higgs-like boson at 125 GeV and assumes that it is the light scalar h of a 2HDM, while the null hypothesis assumes no Higgs boson at all.