Measurement of associated Z+charm production and Search for W' bosons in the CMS experiment at the LHC

Do we understand how elementary particles interact with each other? Are we able to predict the result of the collisions of these elementary particles at the LHC? The objective of this thesis is to investigate the validity of our current theoretical model, the Standard Model of particle physics, to explain the production of two low rate processes in proton-proton collisions at the LHC. The first half of the thesis studies the potential production of new types of interactions, mediated by new W0 bosons, present in many extensions of the Standard Model. This is the first search of this kind at a centre of mass energy of 13 TeV in CMS and uses a dataset of 2.3 fb−1 to search for an excess in the production of events with a muon and large missing transverse energy. As a result of this study, the analysed data is found to be in agreement with predictions of the Standard Model and disfavours the production of new W0 → µν processes. This analysis alone is not able to exclude the production of all kind of W0 interactions. However, it puts strong constrains to its potential cross section and decay to a muon and a neutrino, σW0B(W0 → µν) < 3 fb−1 for W0 masses larger than 2 TeV. In the context of the Sequential Standard Model model, this result excludes W0 SSM bosons with masses smaller than 3.9 TeV. The second part of the manuscript presents the first measurement in CMS of the associated production of Z bosons with charm quarks, Z + c, using 19.7 fb−1 of data collected at 8 TeV. This is a rare process in the Standard Model and its cross section in the studied fiducial region is measured to be σf id(Z + c) = 8.6 ± 0.5 (stat) ± 0.7 (syst) pb. Additionally its relative production to that of bottom quarks, Z + b, is measured to be σ(Z + c)/σ(Z + b) = 2.0 ± 0.2 (stat) ± 0.2 (syst). Both measurements are also determined differentially as a function of transverse momentum of the Z boson and of the heavy flavour jet. Finally these measurements are compared with different theoretical predictions.