Higgs boson mass measurement and study of anomalous quartic gauge-couplings in the four-lepton final state using Large Hadron Collider proton-proton collisions at $\sqrt{s} = 13$ TeV recorded by the ATLAS detector at CERN

In this thesis, three main analyses are presented. First, a short study on the rejection of background for genuine electrons (from prompt decays) is presented, in the context of the ATLAS electron reconstruction and identification. As the main goal of this thesis, a measurement of the Higgs boson mass is presented in the $H\rightarrow ZZ \rightarrow 4l^\pm$ decay channels using Run-2 proton-proton collision data at the Large Hadron Collider corresponding to an integrated luminosity of 139 fb$^{-1}$ at 13 TeV centre-of-mass energy collected by the ATLAS detector. The mass is found to be $m_H = \ensuremath{124.99\pm0.18 \ \text{(stat.)}\pm0.04 \ \text{(syst.)}} \ \mathrm{GeV}$. Also, a combined measurement with the ATLAS Run-1 data is performed, corresponding to approximately 5 fb$^{-1}$ at 7 TeV and 20 fb$^{-1}$ at 8 TeV, where $m_H = \ensuremath{124.94\pm0.17 \ \text{(stat.)}\pm0.03 \ \text{(syst.)}} \ \mathrm{GeV}$. These results were published and can be found in \cite{HIGGSBOSONMASSPUBLICATION}. Finally, a Monte Carlo simulation study is presented, where BSM contributions from anomalous quartic gauge-couplings to $\gamma\gamma\rightarrow 4l^{\pm}$ production are investigated. Assuming a Standard Model only hypothesis, expected upper limits corresponding to a 95\% confidence level are set on effective couplings sensitive to quartic gauge-couplings.