Production of top quarks in association with bosons in the standard model and its extensions, in leptonic final states with the CMS detector at the LHC

This thesis presents measurements where top quarks are produced in association with a Higgs boson or a W boson in final states with leptons. The data used in these studies corresponds to proton-proton collisions recoded by the CMS experiment at the LHC during Run-2, at a centreof- mass-energy of 13 TeV. Standard Model (SM) precision measurements are reported and, in some cases, interpretations on the context of Beyond the Standard Model theories are also carried out. The measurement of the associated production of a Higgs boson with pair of top-antitop quarks (tt̅H) and a single top (tH) is reported in final states targeting the Higgs decay to WW, 𝜏𝜏 and, residually, ZZ. These studies allow to observe tt̅H production with an observed (expected) significance of 4.7 (5.2) standard deviations. Additionally, these processes allow to study the top-Higgs coupling at tree-level. The measurement is interpreted in the context of anomalous couplings. The Higgs-top coupling modifier (𝜅𝑡) is found to be in either one of the intervals − 0.9 < 𝜅𝑡 < − 0.7 and 0.9 < 𝜅𝑡 < 1.1 at 95% confidence level, assuming the rest of the couplings to be those of the SM. The SM Higgs boson is a pseudo-scalar invariant under Charge-Parity (CP) transformations. In this thesis tt̅H process is used to search for CP violation in the top-Higgs coupling. Two dimensional confidence regions are set on 𝜅𝑡 and 𝜅̃𝑡, which are respectively defined as the CPeven and CP-odd top-Higgs Yukawa coupling modifiers. The results are combined with other measurements to include events where the Higgs bosons decays to ZZ and 𝛾𝛾, allowing to set limits on the coupling modifiers, constraining 𝜅𝑡 and 𝜅̃𝑡 to be within (0.86, 1.26) and (-1.07,1.07) at 95% C.L., respectively. The pure CP-odd scenario is excluded with 3.7 standard deviations. The measurement of the associated production of a W boson with pair of top-antitop quarks (tt̅W) is also reported in this thesis. The cross section is measured to be to be 868 ± 40 (stat.) ± 51 (syst.) fb. The reported value is larger than but consistent with the standard model predictions within two standard deviations and represent the most precise measurement of these cross sections to date. Lepton reconstruction, identification, isolation and selection are important items in all the studies presented in this work. In this thesis a new algorithm, based on multivariate analysis techniques is developed and reported. The new algorithm is found to be more performant than the one used during Run-2 and shows a more stable behaviour in conditions with high number of simultaneous collisions.