Search for charginos and neutralinos decaying via a W and a Higgs boson into final states with two same-sign leptons with the ATLAS detector

Supersymmetry as an extension to the Standard Model can solve the hierarchy problem if supersymmetric particles are present at the TeV scale. If R-parity is conserved, the lightest supersymmetric particle is stable and might be a viable dark matter candidate. The production of charginos and neutralinos might be the dominant production mode of supersymmetry at the LHC, if squarks and gluinos are beyond the reach of the LHC. In this thesis, a search for chargino and neutralino production with 36.1 fb$^{-1}$ of $\sqrt{s} = 13 \text{ TeV}$ proton-proton collisions collected with the ATLAS detector is presented. The charginos and neutralinos can decay via W and Higgs bosons into several final states. A final state with exactly two leptons of the same charge, jets and missing transverse energy is analysed. The design of signal regions as well as of validation regions for the WZ diboson background is described. No significant excess over the standard model expectation was observed. Uncertainties considered in the analysis are summarised before interpreting the data in terms of a simplified chargino neutralino model. Chargino masses up to 225 GeV have been excluded for a massless lightest neutralino. Estimating the sensitivity of the analysis using future larger datasets, a maximum discovery significance of 2.92 $\sigma$ was obtained for $\int \mathcal{L} = 140 \text{ fb}^{-1}$.