Higgs boson measurements using di-photon final state signatures and low-mass and di-Higgs boson searches at the ATLAS experiment

The purpose of this project is to perform measurements of the Higgs boson properties, such as the couplings, including self-couplings, using the di-photon channel with data collected by the ATLAS experiment during the Run 3.

Furthermore, additional work will be performed on fast detector simulation, focusing on improving various models for converted photons that will be used extensively in the analysis of the di-photon

channel. This work will likely include the use of machine learning techniques and graph neural networks, to improve the performance of the algorithms.

Additionally, using the data collected during Run 3, a search for low-mass resonances between 60 and 110 GeV will be performed, with the intention to study and compare the ATLAS results to the CMS 95 GeV excess in the di-photon channel. Finally, a search for di-Higgs boson production will be performed, focusing on the bbyy final

state, with the intention to observe trilinear Higgs boson self-coupling and to study the Higgs boson potential, which so far has not been observed.