Measuring the Diphoton Production from Higgs Boson Decays and in Association with Heavy Flavor Jets

In this dissertation, two important measurements are presented related to diphoton production, the differential cross-section measurement of the Higgs boson in the diphoton decay channel as well as a measurement on inclusive diphoton production with associated heavy-flavor jets. Selections between the two analyses are complimentary, making them a natural pairing in the context of this dissertation. The cross-section measurement is performed in a fiducial region of phase space to closely matches experimental selections. This allows for a largely model-independent measurement, providing a meticulous test of the Standard Model as well as other theoretical predictions. The production of diphoton + heavy-flavor jets has never before been measured and initial sensitivity estimates are presented here. This measurement is important as a probe of quantum chromodynamics due to the heavy-flavor jet production, but also as a contributor to other analyses' backgrounds that probe Higgs boson properties. The results presented here were obtained using proton-proton collision data collected by the ATLAS detector using the full Run 2 dataset with a center-of-mass energy of $\sqrt{s} = 13$ TeV at the Large Hadron Collider.