Lawrence Berkeley National Laboratory

Higgsino has been intensively searched for in the LHC experiments in recent years. Currently, there is an uncharted region beyond the LEP Higgsino mass limit where the mass splitting between the neutral and charged Higgsinos is around 0.3-1 GeV, which is unexplored by either the soft di-lepton or disappearing track searches. This region is, however, of great importance from a phenomenological point of view, as many supersymmetric models predict such a mass spectrum. In this Letter, we propose a possibility of filling this gap by using a soft microdisplaced track in addition to the monojet event selection, which allows us to discriminate a signature of the charged Higgsino decay from the standard model background. It is found that this new strategy is potentially sensitive to a Higgsino mass of ≲180(250)  GeV at the LHC Run2 (HL-LHC) for a charged-neutral mass splitting of ≃0.5  GeV.