Precision measurements of the Higgs boson properties: from the H → ZZ* → 4l analysis with CMS at the LHC to the future large lepton colliders

The discussion of this thesis is dedicated to the precision measurements of the Higgs (H) boson properties, spanning from the study of the H boson decaying into four leptons with the CMS experiment at the Large Hadron Collider (LHC) to the future investigation of the H boson sector at large lepton colliders. The H → ZZ* → 4l (l=e,μ) decay channel offers an optimal way to study the H boson profile, playing a central role since the time of the discovery. Properties of the H boson are measured exploiting the total amount of data produced in proton-proton collisions at the LHC during Run 2. The dataset collected by the CMS experiment at a center-of-mass energy of 13 TeV corresponds to an integrated luminosity of 137 fb−1. The inclusive signal strength modifier and the signal strength modifiers for the main H boson production modes are reported. In addition, results within the framework of the Simplified Template Cross Sections are produced to explore the different H boson production mechanisms in specific kinematic regions of the phase space. The inclusive fiducial cross section for the H → 4l process is presented and the differential cross sections as a function of the transverse momentum and rapidity of the four-lepton system, the transverse momentum of the leading jet, and the jet multiplicity are shown. All results are found to be in agreement with the SM predictions. Along the way, the perspectives offered by future colliders in the exploration of the Higgs sector and an overview of the different projects of future machines and experiments are also presented. A large focus is reserved for the ongoing development of the design of a detector proposal called IDEA (Innovative Detector for Electron-positron Accelerators), specifically intended for the future H boson factory colliders.