Search for flavor-changing neutral-current interactions between the top quark and the Higgs boson in dileptonic same-charge final states with the ATLAS detector

The analysis presented in this thesis focuses on the search for flavor-changing neutral-current (FCNC) interactions involving the top quark and the Higgs boson at a center-of-mass energy of $\sqrt{s}=13\,$TeV with the ATLAS detector. These interactions are searched for in the production of a top-quark-antiquark pair, with one top quark decaying via anomalous couplings into a Higgs boson and either a $c$-quark or a $u$-quark. This particular analysis examines leptonic decay modes of the Higgs boson, with final states containing exactly two leptons of the same charge. As a primary step in the analysis strategy, kinematic regions enriched in FCNC events are identified. Neural networks are trained in those regions to most efficiently discriminate the FCNC process from background processes. Due to the rarity of final states with two leptons of the same charge, a large fraction of background processes contains leptons which either originate from hadronic jets or are reconstructed with an inverted charge. Various tools to reduce the contribution of those background processes are studied and applied. Additionally, specific kinematic regions enriched in either of the background processes are identified. They are used in a template fit to data to correct the estimated rates of these processes. Under the inclusion of statistical and most systematic uncertainties, expected upper limits on the branching ratios of the considered FCNC processes are determined via a global binned profile likelihood fit. They amount to $\mathcal{B}(t\rightarrow uH)=3.7\times10^{-4}$ and $\mathcal{B}(t\rightarrow cH)=3.9\times10^{-4}$, respectively.