With the start of the second running phase (Run 2) of the Large Hadron Collider (LHC) at CERN, the study of the fundamental constituents of matter has again entered an exciting time. The observation of a Higgs-like boson at the LHC seems to confirm a central prediction of the Standard Model (SM) of particle physics. All properties of the discovered particle need however to be accurately determined to establish whether the new particle is the Higgs boson predicted in the SM.The proposal aims at studying the couplings of the Higgs boson to fermions, which in the SM gives rise to masses of quarks and leptons. These couplings allow the Higgs boson to decay into fermions. No such decay has however been observed yet. This projects targets an observation of the Higgs boson decay into a pair of b quarks, and a precise measurement of this decay rate using the full dataset to be acquired by the CMS detector during Run 2. A lack of observation of this decay or a deviation of its rate from the SM expectation would point at the presence of physics beyond the SM and be of great significance. The project also aims at direct searches for new particles by studying final states with b quarks.The project also intends to contribute to the improved performance of the CMS detector by improving the identification of hadronic jets stemming from the hadronization of a b quark (b-jets). The identification of b-jets (B tagging) will in particular benefit from the installation of an upgraded silicon pixel detector in early 2017. One of the project goals consists in optimizing the B tagging performance using the features of the upgraded detector, with a special focus on the tagging of topologies in which two very energetic b-jets are merged in one so-called “fat jet”. This relies on a good integration of the upgraded pixel detector in the CMS measurements, and the project therefore also includes a set of objectives linked to the improvement of the pixel detector performance and reconstruction.