Reach of e^+e^- Higgs factory for light higgsinos via electroweak precision observables and comparison with other future facilities

Abstract: Light higgsinos with mass ~100-400 GeV are well-motivated from naturalness considerations within supersymmetric models. However, at hadron colliders such as CERN LHC, they are rather difficult to search for due to the small visible energy release from heavy higgsino decay to the lightest higgsino, assumed here to be the lightest SUSY particle (LSP). An alternative way to search for the sparticles of supersymmetry is via their virtual effects on electroweak precision observables (EWPO) such as the W boson mass or the effective weak mixing angle \sin^2\theta_{\rm eff}. We quantify the ability of an e^+e^- Higgs factory operating at \sqrt{s}\sim 90-250 GeV to indirectly detect higgsinos via EWPO in the so-called higgsino discovery plane. The latter allows one to compare the relative reach of LHC and high-lumi LHC with an e^+e^- Higgs factory and with a linear e^+e^- collider operating at \sqrt{s}~ 0.5 TeV.