Hunting ewinos and a light scalar of Z3-NMSSM with a bino-like dark matter in top squark decays at the LHC

We explore a possible signal of the presence of relatively light electroweakinos (ewinos) and a singlet-like scalar (aS) of the Z3-symmetric Next-to-Minimal Supersymmetric Standard Model (Z3-NMSSM) in the cascade decays of not so heavy top squarks ( m_t̃_1 ≲ 1.5 TeV) that may be produced in pairs at the Large Hadron Collider LHC. We work in a scenario where the lightest (next-to-lightest) SUSY particle is bino (singlino)-like with its mass below 100 GeV and is mildly tempered with higgsino and singlino admixtures. The singlet-like scalar provides an annihilation funnel for the bino-like states such that the latter could act as a viable dark matter candidate, unlike what is now highly constrained in the MSSM. We consider a pair of immediately heavier neutralinos and the lighter chargino which all are higgsino-like with masses in the range 0.5–1 TeV and are still compatible with all experimental constraints. While these states may not be accessible in their direct searches at the LHC in our present scenario, such ewinos could still be traced in the decays of the top squarks of the above-mentioned kind. We consider the signal final state at the LHC. We find that while a usual cut-based analysis (CBA) of LHC data worth 300 fb−1 would be unable to discover such excitations, a multivariate analysis (MVA) can be reasonably sensitive to higgsino-like ewinos having masses ≳ 650 GeV when m_t̃_1 ≳ 1 TeV. On the other hand, with 3000 fb−1 of data, these masses become accessible in a CBA while even an MVA on such a data set is unlikely to find these ewinos with masses around 1 TeV when m_t̃_1 hits ∼ 1.5 TeV.