HL-LHC sensitivity to higgsinos from natural SUSY with gravitino LSP

In the realm of natural supersymmetric models, higgsinos are typically the lightest electroweakinos. In gauge-mediated supersymmetry breaking models, the lightest higgsino-dominated particles decay into a Z -boson or a Higgs boson ( h ), along with an ultra-light gravitino ( G̃ G ~ ) serving as the lightest supersymmetric particle (LSP). This scenario suggests a significant non-resonant hh production. Basing on the recent global fitting results of the G̃ G ~ -EWMSSM (MSSM with light electroweakinos and an eV-scale gravitino as the LSP) performed by the collaboration, which support a higgsino-dominated electroweakino as light as 140 GeV, we develop two simplified models to evaluate their detection potential at the high-luminosity LHC (HL-LHC) with √s = 14~TeV s = 14 TeV and an integrated luminosity of 3000~fb⁻¹ 3000 fb - 1 . The first model examines the processes where heavier higgsino-dominated states decay into soft W / Z bosons, while the second focuses on direct decays of all three higgsino-dominated electroweakinos into W / Z / h plus a G̃ G ~ . Our study, incorporating both models and their distinct decay channels, utilizes detailed Monte Carlo simulations for signals and standard model backgrounds. We find that the HL-LHC can probe higgsinos up to 575 GeV, potentially discovering or excluding the natural SUSY scenario in the context of a gravitino LSP. Further, we reinterpret this discovery potential using the GAMBIT global fit samples, and find that the entire parameter space of |μ | ≤ 500~GeV | μ | ≤ 500 GeV with an electroweak fine-tuning measure ( Δ EW Δ EW ) under 100 in G̃ G ~ -EWMSSM is accessible at the HL-LHC.