Electroweakinos in the light of the Higgs boson

Given the increasingly more stringent bounds on supersymmetry (SUSY) from the LHC searches, we are motivated to explore the situation in which the only accessible SUSY states are the electroweakinos (charginos and neutralinos). In the minimal SUSY framework, we systematically study the three general scenarios classified by the relative size of the gaugino mass parameters M₁ and M₂ and the Higgsino mass parameter μ, with six distinctive cases, four of which would naturally result in a compressed spectrum of nearly degenerate lightest supersymmetric particles. We present the relevant decay branching fractions and provide insightful understanding about the decay modes in connection with the Goldstone-boson equivalence theorem. We show the cross sections for electroweakino pair production at the LHC and International Linear Collider and emphasize the unique signals involving the Standard Model-like Higgs boson as a new search reference. The electroweakino signal from pair production and subsequent decay to the Wh/Zh(h→bb̄) final state may yield a sensitivity of 95% C.L. exclusion (5σ discovery) to the mass scale M₂, μ∼350-400 GeV (220-270 GeV) at the 14 TeV LHC with a luminosity of 300 fb^-1. Combining with all the other decay channels, the 95% C.L. exclusion (5σ discovery) may be extended to M₂, μ∼480-700 GeV (320-500 GeV). At the ILC, the electroweakinos could be readily discovered once the kinematical threshold is crossed, and their properties could be thoroughly studied.