The compressed bino--wino dark matter in the GmSUGRA and the LHC soft-lepton searches

Abstract

The search for electroweak supersymmetric particles remains an important part of the LHC program since neutralinos and charginos with masses around a few hundred GeV are still compatible with the present constraints in compressed spectra. Run-2 searches for the ``golden channel'', $pp\to\widetildeχ_2^0\widetildeχ_1^\pm\to\widetildeχ_1^0 Z^{(*)}\widetildeχ_1^0 W^{\pm(*)}$, have reported mild excesses in parts of the soft two- and three-lepton data, with the corresponding simplified-model interpretations emphasizing $m_{\widetildeχ_2^0}\simeq m_{\widetildeχ_1^\pm}\gtrsim200$~GeV and a neutralino mass difference near $20$~GeV. We study this configuration in the Minimal Supersymmetric Standard Model (MSSM) with the Generalized minimal Supergravity (GmSUGRA) boundary conditions, imposing the Higgs, flavor, collider, relic-density and direct-detection constraints relevant to the spectrum. For both signs of $μ$, the solutions compatible with the Planck experiment contain an almost pure bino $\widetildeχ_1^0$ with mass about $260$--$266$~GeV and a nearly degenerate wino-like $\widetildeχ_2^0/\widetildeχ_1^\pm$ pair near $280$~GeV. The resulting splitting, $Δm_{21}\simeq18.5$--$19.1$~GeV, lies in the mass-difference region probed by the ATLAS and CMS soft-lepton searches and places the $Z^{(*)}/W^{(*)}$ decays below the on-shell gauge-boson thresholds. The same compressed hierarchy keeps the wino states thermally populated during freeze-out, so bino-wino coannihilation yields a neutralino relic abundance consistent with the Planck experiment while the surviving solutions remain compatible with the direct-detection experimental bounds. Thus, the GmSUGRA boundary conditions provide a high-scale realization of the compressed bino-wino spectrum relevant to the LHC soft-lepton channel.