Search for an extended scalar sector through the H$ \to$ ZA $\to$ $\ell^+ \ell^- b\bar{b}$ process in pp collisions at $\sqrt s=13$ TeV

The validity of the Standard Model (SM) of particle physics, has been remarkably proven by a large programme of experimental researches, culminating in the discovery of the Higgs boson in 2012 at CERN. Despite this, the existence of new physics is strongly suggested by the inability of the SM to explain in a satisfactory way some observed phenomena, such as the existence of dark matter and the matter/antimatter asymmetry in the Universe. To overcome these problems, many theoretical models beyond the SM predicting the existence of new particles are postulated. Among these, the two-Higgs-doublet model (2HDM) is one of the simplest extensions of the SM scalar sector, and entails the presence of five new bosons. In this thesis, the search for two of these particles, H and A, is presented. The search is performed through a statistical analysis of the data collected by the CMS experiment at the CERN Large Hadron Collider (LHC) during 2016 at a center-of-mass energy of 13 TeV and integrated.