Projection studies of Higgs boson pair production to the 4 b-jet final state at the HL-LHC using the ATLAS detector

Projection studies for the non-resonant Higgs boson pair production in the $\bbbb$ final state with the ATLAS detector at the HL-LHC are presented. They are based on extrapolated results of the latest Run 2 analysis which targeted both the gluon-gluon fusion and vector-boson fusion Higgs boson pair production modes and exploited \SI{126}{\ifb} of $\sqrt{s} = \SI{13}{\tev}$ data. The projection assumes an integrated luminosity of \SI{3000}{\ifb} for HL-LHC proton-proton collisions at $\sqrt{s} = \SI{14}{\tev}$. Various systematic uncertainty scenarios are explored. With (without) systematic uncertainties, the discovery significance of the Standard Model Higgs boson pair production is found to be $1.0\sigma$ ($1.8\sigma$), while the 95\% confidence-level upper limit on the \HH signal strength is set at $2.0$ ($1.1$). The allowed 68\% confidence-interval for the \HHH coupling modifier $\kl$ is found to be $[-0.5, 6.1]$ ($[0.1, 2.6]$), while the allowed 68\% confidence-interval for the \HHVV coupling modifier $\kTwoV$ is $[0.7, 1.4]$ ($[0.7. 1.3]$).