Updated projection of the sensitivity of searches forHiggs boson pair production in the bb̄γγ final statefrom LHC Run 2 to the High Luminosity LHC withthe ATLAS detector

The search for Higgs boson pair production ($HH$) is one of the leading priorities for the physics program at the High-Luminosity LHC (HL-LHC). This rare process provides access to the Higgs boson self-coupling. ATLAS has performed searches for $HH$ production in a variety of final states with the LHC Run 2 dataset and has set combined observed (expected) upper limits on the cross section for this process of 2.9 (2.4) times the Standard Model prediction. The most recent ATLAS HH → bb̄γγ analysis, using the full Run 2 dataset, contributed to this combination, yielding observed (expected) limits of 4.0 (5.0). This note describes an extrapolation of the latest ATLAS HH → bb̄γγ search to the expected luminosity and conditions at the HL-LHC. For the benchmark case, with 3000\ fb⁻¹ at √s=14 TeV, this resulted in a projected significance of $2.4$ standard deviations and a $45%$ uncertainty on the $HH$ signal strength, assuming the Standard Model. This corresponds to a projected constraint on the Higgs boson self-coupling parameter κλ of -0.1 < κλ < 3.4.