Search for BSM Higgs bosons in final states with b-quarks with the full Run 2 CMS dataset

This thesis presents the search for heavy neutral Higgs bosons, produced in associationwith b-quarks and decaying into a b-quark pair in proton-proton collisions at a centre-ofmass energy of 13 TeV at the LHC with the CMS detector. The process is chosen, giventhat a considerable enhancement of the coupling to b-quarks is possible in theories beyondthe Standard Model, such as the Minimal Supersymmetric extension of the StandardModel (MSSM) and the Two Higgs Doublet Model (2HDM). A new boson would manifestitself as an excess in the invariant mass distribution of the two leading b-tagged jets. Thefinal state is rather challenging, requiring dedicated triggers to control the large rate ofmultijet backgrounds. The data used in this thesis was collected during 2017 and 2018 andcombined with a previous search in the same channel with 2016 data to provide resultsusing the full Run 2 dataset, accounting for up to 127 fb???1 of data.The search is performed for several mass hypotheses in two categories. In one, it isconducted in a fully-hadronic category, which is sensitive only to masses above 300 GeVand limited by trigger rates. Sensitivity to lower masses is recovered in the semi-leptoniccategory, in which a muon is required within a final state jet, reducing the trigger rateswith low transverse-momenta jets.Special attention is given to the background modelling, for which a data-driven approach has been used, and efforts have been made to reduce the uncertainties. In addition,a new modified event selection yields significant enhancements in the signal efficiency andoverall significance compared to previous analyses.These improvements enabled the exploration of masses up to 1.8 TeV, a significantextension compared to existing results. The sensitivity towards lower masses was extended to 125 GeV with the SL category. No significant deviation with respect to thebackground-only hypothesis was observed, and upper limits were set on the cross-sectiontimes branching ratio of the scrutinized process at 95% confidence level. These limits aretranslated into exclusion limits in the parameter space of MSSM and 2HDM benchmarkscenarios. These are the most stringent limits to date on this process.