Measurement of Higgs boson properties in the diphoton decay channel and a search for di-Higgs production in the gamma gamma b anti-b final state with the ATLAS detector

This thesis presents two physics analyses performed with the ATLAS detector at the Large Hadron Collider. Proton-proton collision data was used, corresponding to an integrated luminosity of 36.1 1/fb, obtained at a center-of-mass energy of 13 TeV, during 2015 and 2016. The first analysis is a search for resonant and non-resonant Higgs boson pair production in the gamma gamma b anti-b final state. The second one is the measurement of the total Higgs boson production-mode cross sections, signal strengths, and simplified template cross sections, as well as the measurement of the fiducial and differential cross sections in the diphoton decay channel. Special emphasis is given to the strategy followed to estimate the uncertainty in the modeling of the parton shower, underlying event and hadronization. The reconstruction and identification techniques of the relevant objects such as photons and jets are covered extensively, and a validation of the calorimeter energy scale is performed by using the ATLAS Tile Calorimeter response to single hadrons with proton-proton collision data obtained at center-of-mass energies of 7 and 8 TeV, during 2010–2012 with the ATLAS detector.