Prospect studies for Higgs boson pair production to $b$$\bar{b}$$\gamma\gamma$ final state at the HL-LHC with the ATLAS detector

By the end of the HL-LHC era, before 2040, the ATLAS experiment aims to increase the size of the dataset from ∼300fb$^{−1}$, acquired at the end of LHC running, up to ∼3000fb$^{−1}$. The large dataset expected after HL-LHC operation increases the likelihood of seeing rare processes such as the $H$ → $HH$ → $b$$\bar{b}$$\gamma\gamma$ decay channel. This channel is one of the most promising for measuring the Higgs boson self-coupling. To mimic the expected ATLAS detector response to various physics objects at the HL-LHC, upgrade performance functions are constantly developed and updated. A recent update to these functions included the addition of a considerably more realistic estimate of the expected material budget of the ITk, as well as dedicated functions for both the 50×50$\mu$m$^{2}$ and 25×100$\mu$m$^{2}$ pixel sensor geometries. A Boosted Decision Tree method was applied to the $H$ → $HH$ → $b$$\bar{b}$$\gamma\gamma$ channel to determine the effects of these changes. It was shown that the more realistic material budget and dedicated 50×50$\mu$m$^{2}$ functions result in a significance for observing this channel of 3.10±0.13. Comparable results are obtained when using either a pixel sensor geometry of 25×100$\mu$m$^{2}$ or reducing the radius of the innermost pixel layer.