Measurement of differential cross-sections for Higgs boson production in the $\gamma \gamma$ decay channel at $\sqrt{s}$ = 13TeV with the ATLAS experiment

The analysis presented in this work is based on the full proton-proton collision dataset recorded at center-of-mass energy of 13 TeV by the ATLAS experiment (the so-called Run2, amounting to an integrated luminosity of 139 $fb^{−1}$ ) at the Large Hadron Collider (LHC) during the period 2015-2018. This thesis is about the measurement of the differential fiducial cross sections of Higgs boson production, for several observables, based on the di-photon $H \rightarrow \gamma\gamma$ decay channel. This channel, although penalized by a low Branching Ratio ($2.27 \times 10^{−3}$) compared to other decay channels, has the advantages of a good efficiency, a fully reconstructed final state, and a very good invariant mass resolution of the Higgs peak. In this thesis, the full analysis is described with some original additions and variations with respect to the standard ATLAS published papers. Moreover, I’ve performed an extrapolation to a higher integrated luminosity, in order to study the future High-Luminosity LHC (HL-LHC) performance and how the larger statistics will affect the total error.