Search for new physics in events with two Higgs bosons and missing transverse momentum in $\sqrt{s}=13\;\text{TeV}$ $pp$ collisions at the ATLAS experiment

A search is presented for pair production of higgsinos, the supersymmetric partners of the Higgs bosons, in scenarios with gauge-mediated supersymmetry breaking. Each higgsino is assumed to decay into a Higgs boson and a nearly-massless gravitino. The search targets the decay of the two Higgs bosons to $b\bar{b}$, leading to a reconstructed final state with at least three energetic $b$-jets and missing transverse momentum. Two complementary analysis channels are used, with each channel specifically targeting either low or high values of the higgsino mass. The low (high) mass channel exploits 126 (139) $\mbox{fb\(^{-1}\)}$ of $\sqrt{s}={13}$ ${\text{TeV}}$ data collected by the ATLAS detector during the Run 2 of the Large Hadron Collider. No significant excess above the Standard Model prediction is found. At 95% confidence level, masses are excluded up to ${950}$ ${\text{GeV}}$ for higgsinos decaying exclusively to Higgs bosons. Exclusion limits as a function of the higgsino decay branching ratio to a $Z$ or a Higgs boson are also reported.