Мерење односа гранања Хигсовог бозона за распад на пар Z бозона на енергијама 350 GeV и 3 TeV на Компактном линеарном сударачу CLIC

The CLIC is an option of a future e$^+$e$^-$ linear collider at CERN that will run at three energy stages: 380 (350) GeV, 1.5 TeV and 3 TeV. It offers a rich Higgs physics programme as well as the possibility to probe new physics models up to a 100 TeV scale. Lowest energy stage allows precise measurement of the Higgsstrahlung cross-section ($\sigma_{\mathrm{HZ}}$) which is input for the model-independent determination of Higgs couplings from the measured $\sigma_{\mathrm{HZ}}$ x BR observable. Higher energy stages enable access to measure rare Higgs decays providing enhaced sensitivity to realization of the physics beyond Standard Model. The Higgs coupling to Z bosons can be determined with the relative statistical precision below 1% from a global fit of measurements collected at all energy stages of CLIC. This thesis presents the full simulaton of experimental measurement of the Higgs branching fraction BR($H\rightarrow ZZ^{*}$) at 350 GeV and 3 TeV centre-of-mass energies at CLIC. The semileptonic final state of the signal is considered at both energies, assuming integrated luminosities of 1 ab$^{-1}$ at 350 GeV and 5 ab$^{-1}$ at 3 TeV centre-of-mass energies and unpolarised beams. The signal is separated from background by applying multiphased selection including multivariate analysis based on the Boosted Decision Tree. It is found that the Higgs branching ratio BR($H\rightarrow ZZ^{*}$) can be measured with the relative statistical uncertainty of (1 $\pm$ 0.030) BR$_{\mathrm{SM}}$ and (1 $\pm$ 0.20) BR$_{\mathrm{SM}}$ at 68% CL, at 3 TeV and 350 GeV centre-of-mass energies, respectively. Due to the chiral nature of WW-fusion statistical precision at 3 TeV centre-of-mass energy can be enhanced by a factor $\sim \sqrt 1.5$ by applying 80% longitudinal electron beam polarisation.