Updated projection of the sensitivity of searches forHiggs boson pair production in the bb 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 bb 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 bb 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 _ of -0. 1 < _ < 3. 4.