This thesis focuses on the exploration of potential new physics (NP) searches and a better understanding of the Standard Model (SM) at future colliders. Despite the discovery of the Higgs Boson, there is still no strong evidence for NP in collider experiments in the past decade. One possible explanation for this is the limited ability of existing colliders. First part of this thesis is dedicated to the study on Lepton Flavour Universality (LFU) at future Z-factories. This includes precision measurements on R_J/ψ, R_D*s , R_Ds and R_Λc ratios. The results are combined with other measurements on b → cτν, b → sτ⁺τ⁻ and b → sνν̄ to interpret NP using SM Effective Field Theory framework. Discussions are also included on the effects of vertex uncertainties, ECAL resolution, and extra global event...[ Read more ]

This thesis focuses on the exploration of potential new physics (NP) searches and a better understanding of the Standard Model (SM) at future colliders. Despite the discovery of the Higgs Boson, there is still no strong evidence for NP in collider experiments in the past decade. One possible explanation for this is the limited ability of existing colliders. First part of this thesis is dedicated to the study on Lepton Flavour Universality (LFU) at future Z-factories. This includes precision measurements on R_J/ψ, R_D*s , R_Ds and R_Λc ratios. The results are combined with other measurements on b → cτν, b → sτ⁺τ⁻ and b → sνν̄ to interpret NP using SM Effective Field Theory framework. Discussions are also included on the effects of vertex uncertainties, ECAL resolution, and extra global event shape information on the ratio measurements. Second part of this thesis focuses on the search on Heavy Neutral Lepton (HNL) at the future muon colliders. This aims to provide exclusion limit on currently undiscovered parameter space. Additionally, the study investigats distinguishing Majorana and Dirac nature of the HNL. Overall, this thesis contributes to the understanding of the SM and the search for NP at future colliders. The precision measurements and exclusion limits presented in this thesis can guide future experiments in the search for new physics beyond the Standard Model.