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

Abstract

Abstract 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 ( $$\tilde{G}$$ 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 $$\tilde{G}$$ G ~ -EWMSSM (MSSM with light electroweakinos and an eV-scale gravitino as the LSP) performed by the GAMBIT 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 $$\sqrt{s} = 14~\textrm{TeV}$$ s = 14 TeV and an integrated luminosity of $$3000~\textrm{fb}^{-1}$$ 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 $$\tilde{G}$$ 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 $$|\mu | \le 500~\textrm{GeV}$$ | μ | ≤ 500 GeV with an electroweak fine-tuning measure ( $$\Delta _{\textrm{EW}}$$ Δ EW ) under 100 in $$\tilde{G}$$ G ~ -EWMSSM is accessible at the HL-LHC.