Cornering Higgsino: Use of Soft Displaced Track

Abstract

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 micro-displaced track on top of the mono-jet 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 $\lesssim 180$ $(250)$ GeV at the LHC Run 2 (HL-LHC) for a charged-neutral mass splitting of $\simeq 0.5$ GeV.