Search for dark matter produced in association with a Higgs boson decaying to a pair of bottom quarks in proton-proton collisions at $\sqrt{s} =$ 13 TeV using CMS 2017 and 2018 data

The discovery of the Higgs boson has opened a new portal to search for Dark Matter(DM). Since DM does not interact in the CMS detector, searches rely on the missing transverse energy in association with a visible SM particle. The final state of the Higgs boson+missing transverse energy is known as ”mono-Higgs”. In this thesis, mono-Higgs analysis has been performed in two categories; Boosted and Resolved. In the first part of the thesis, we present a search for DM when it is produced in association with a highly boosted Higgs boson decaying to a pair of bottom quarks in proton-proton collisions at $\sqrt{s}=13$TeV using data collected at CMS detector in 2017 and 2018, corresponding to a total luminosity of 101.3 ${fb}^{-1}$. The Higgs boson is reconstructed using a fatjet (AK8jet), and the decay to $b\bar{b}$ quarks is identified using the DeepDoubleB tagger algorithm. This category targets the phase space where the DM-SM mediator mass is high. Two sensitive observables, missing energy and mass of the Higgs boson, are used for this search. Finally, we compare observed and expected events and interpret results in terms of the upper limit in the context of three signal models: 2HDM+a, Z’-2HDM and Baryonic-Z’.\\ In the second part of the thesis, we present a search for DM when it is produced in association with a low or medium-boosted Higgs boson decaying to a pair of bottom quarks in proton-proton collisions at $\sqrt{s}=13$TeV using data collected at CMS detector in 2017 and 2018 corresponding to a total luminosity of 101.3 ${fb}^{-1}$. Higgs boson is reconstructed using two narrow jets (AK4jets), and deepCSV algorithm is used to identify b quarks. This category targets the phase space where DM-SM mediator mass is low. The observables of missing energy and mass of the Higgs boson are used for this search. Results are interpreted in terms of the upper limit in the context of three signal models: 2HDM+a, Z’-2HDM and Baryonic-Z’.Finally, we present the combination of resolved and boosted categories results for all three models and show a projection of this search for Run3 and HL-LHC in the context of 2HDM+a model.