Studies of the Higgs Sector with the CMS experiment at the LHC and at Future Hadron Colliders

The discovery of the Higgs boson at the Large Hadron Collider (LHC) marked a cornerstone in particle physics, completing the Standard Model description of electroweak symmetry breaking. Nonetheless we still know very little about it: the structure of the scalar potential, the possible existence of additional Higgs bosons, and the nature of the Higgs self-interaction are still largely unknown. These questions are central to understanding whether the Higgs boson is a solitary particle or part of a richer scalar sector, and whether it may provide a portal to physics beyond the Standard Model.

This thesis presents studies of the Higgs sector carried out with the CMS experiment at the LHC and in the context of future hadron colliders. Using data from CMS, I worked on the search for two new  Higgs bosons, focusing on the process where the heavier of the two decay into the lighter one together with a Z boson. Complementary to this, I worked on projections for Higgs boson pair production, a process directly sensitive to the Higgs self-coupling, at upcoming hadron colliders. These include the High-Luminosity LHC, the next phase of the LHC program, and the proposed Future Circular Collider (in its proton-proton stage), a leading candidate for the next-generation collider facility.

Together, these studies probe both the presence of new Higgs-like particles and the structure of the Higgs potential, illustrating the current and future opportunities at collider experiments to address the pressing open questions in fundamental physics.