Abstract: Astrophysical evidence supports the existence of dark matter based on its gravitational interaction. Astrophysical evidence also points to that dark matter interacts at most very weakly with the standard model particles. The only purely weakly interacting particles in the standard model are neutrinos, which have too low a mass to be the dark matter candidates. Therefore, there is compelling motivation for physics beyond the standard model which contains weakly interacting massive particles. Many beyond the standard model theories predict the existence of dark matter particle candidates that can be produced and detected at high energy colliders, driving experimental searches at the CERN LHC.
This thesis presents a search for dark matter particles produced in association with a Higgs boson in proton-proton collisions at 13 TeV. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 101 /fb. Higgs decay to a bottom quark-antiquark pair is reconstructed to identify events of interest. The analysis is performed in exclusive categories targeting both Lorentz-boosted (merged) and resolved b-pair topologies, covering a wide range of Higgs boson transverse momentum. This analysis looks for statistically significant deviations from the standard model predictions, either enhancements in specific kinematic regions or a bump in the b-pair invariant mass distribution. The observed data agree with the standard model background predictions. Constraints are placed on dark matter models predicting new particles or interactions, such as those in the simplified frameworks of baryonic-Z' and 2HDM+a. A statistical combination is made with a previous search using data collected in 2016 and corresponding to an integrated luminosity of 35.9 /fb. Upper limits at 95% confidence level are set on the production cross section for these models. These results improve upon the previously existing LHC limits owing to the larger integrated luminosity and improved identification of h-->bb decay. Potential improvements from an ongoing CMS search using the Run-3 data are discussed, along with the future prospects at a high energy muon collider.