Simulation Study of Invisible Decays of the Higgs Boson with the Circular Electron Positron Collider

A Higgs-like boson has been discovered by the experiments ATLAS and CMS at the LHC. We need to verify that it is the Standard Model (SM) Higgs and understand its nature. A Circular Electron Positron Collider (CEPC), has been proposed as a Higgs factory for detailed study of the Higgs boson. In this dissertation we study the feasibility of measuring the H → Invisible decays at the CEPC. Dark Matter (DM) interacts with matter by gravity, thus appears to be invisible in the CEPC experiment. If Higgs boson couples to DM it could be an important “portal” to New Physics. A Monte Carlo analysis of H → Invisible optimized to achieve high signal significance, and low backgrounds in the e+e− → ZH, Z → µ+µ− channel based on an integrated luminosity of 5 ab−1 expected for ten years run of the CEPC, is performed. Precision on the Higgs to invisible branching ratio at the input values of 0.1%(SM) and Beyond Standard Model (BSM) cases 0%, 1%, 5% and 10% is determined. Two approaches have been employed. They are the cut-based analysis and the multivariate analysis. Based on this dissertation study a baseline analysis approach is recommended for future CEPC design and studies.