Метод мерења односа гранања Хигсовог бозона $ BR(H\to \gamma \gamma )$ на 3 ТеV CLIC

In this thesis is addressed the potential of the Compact Linear Collider (CLIC) operating at 3 TeV center-of-mass energy to measure branching fraction of Higgs boson decay to two photons $BR(H\to \gamma \gamma )$, with 5 $ab^{-1}$ of integrated luminosity. Since photons are massless, Higgs boson coupling to photons is realized through higher order processes involving the heavy particles either from the Standard Model or beyond. Any deviation of the measured $BR(H\to \gamma \gamma )$ and consequently of the Higgs coupling $g_{H\gamma \gamma }$ from the predictions of the Standard Model, may indicate New Physics. The Higgs decay to two photons is thus an interesting probe of the Higgs sector at future Higgs factories. The study is performed using the full simulation of а detector for CLIC and by considering relevant physics and beam-induced processes in a full reconstruction chain. Multivariate analysis is employed to separate signal from background, while the shape of the reconstructed di-photon invariant mass distribution is described with the probability density functions (PDFs) for signal and background. Pseudo-data are fitted with PDFs to extract the number of signal events. It is found that, once the Higgs production cross section in WW-fusion is known, $BR(H\to \gamma \gamma )$ can be measured with a relative statistical uncertainty of 5.5% at the confidence level of 68%.