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Associated production of Dark Matter with heavy fermions at the RUN3 of the LHC

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Resumo:Dark matter (DM) stands as one of the most prominent mysteries that the Standard Model of Particle Physics (SM) has yet to unravel. Several compelling observations indicate the existence of non-baryonic matter in the Universe, which interacts solely through gravitational forces with ordinary matter. Assuming the presence of a new interaction mechanism, three distinct search approaches have arisen, with collider-based searches demonstrating notable potential for uncovering and characterizing the nature of DM. In this thesis, a search is undertaken to explore possible DM particles concealed within the final states of the tt̅ topology. Within the framework of the simplified DM models, this phenomenological analysis involves the reconstruction of a tt̅ system considering the presence of a spin-0 mediator denoted as Y0 that couples to both SM and DM particles. Signal samples of pp → tt̅ Y0 are generated at Next-to-Leading Order (NLO), considering both Charge-Parity (CP)-even and CP-odd couplings of Y0 to the top quarks. The MadGraph5_aMC@NLO framework is employed for this purpose. Various mass scales for the mediator Y0 are explored, ranging from an ultra-low mass region (approximately 0 GeV) to the mass of the Higgs boson (125 GeV). The analysis concentrates on the dileptonic final states of the tt̅ system, while accounting for all relevant SM background processes associated with the dileptonic tt̅ search at the LHC. An event reconstruction algorithm is applied to both signal and background SM samples to reconstruct solely the tt̅ system. Additionally, new CP angular observables are utilized to probe the CP-nature of the coupling between the mediator and top quarks. This leads to the establishment of confidence level (CL) limits for the Yukawa couplings as functions of the mediator mass.
Autores principais:Silva, Rui Miguel Dinis
Assunto:CP Violation Dark Matter Top Quark LHC Phenomenology Violação de CP Matéria escura Quark Top Fenomenologia
Ano:2023
País:Portugal
Tipo de documento:dissertação de mestrado
Tipo de acesso:acesso aberto
Instituição associada:Universidade do Minho
Idioma:inglês
Origem:RepositóriUM - Universidade do Minho

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