Consistent Excesses in the LHC Electroweak SUSY Searches: GUT-based Singlino/Higgsino Interpretation in the NMSSM

Abstract

The search for supersymmetric models remains one of the main items on the BSM search program at the LHC, with EW SUSY partners still allowed with masses as low as a few hundred GeV. Over the last years, searches for the "golden channel", $pp \to \tilde{\chi}^0_2 \tilde{\chi}^{\pm}_1 \to \tilde{\chi}^0_1 Z^{(*)} \tilde{\chi}^0_1 W^{\pm (*)}$ show consistent excesses between ATLAS and CMS in the 2~soft-lepton and 3~soft-lepton plus missing-$E_T$ searches, assuming $m_{\tilde{\chi}^0_2} \approx m_{\tilde{\chi}^{\pm}_1} \gtrsim 200$ GeV and $\Delta m_{21} := m_{\tilde{\chi}^0_2} - m_{\tilde{\chi}^0_1} \approx 20$ GeV. We interpret these excesses in the framework of the Next-to-Minimal Supersymmetric Standard Model. We assume a singlino dominated lightest neutralino as a Dark Matter (DM) candidate. The second and third lightest neutralinos are higgsino like, with the higgsino mixing parameter $\mu$ being smaller than the soft SUSY-breaking bino and wino masses, $M_1$ and $M_2$. We furthermore assume the approximate GUT relations $M_1 \sim M_2/2 \sim M_3/6$, with the implication for our scenario of a gluino mass $m_{\tilde{g}} \sim M_3 \gtrsim 3$ TeV. Scalar masses are assumed to heavy and do not play a role in our analysis. We find that this scenario is in agreement with all relevant experimental constraints, comprising the LHC searches for SUSY particles and additional Higgs bosons, the LHC Higgs-boson rate measurements, the DM direct detection limits and the upper limit on the DM relic density. We demonstrate that this scenario gives an excellent description of the observed excesses in the search for 2~and 3~soft-leptons plus \ETmiss, with $m_{\tilde{\chi}^0_2} \sim m_{\tilde{\chi}^0_3} \sim m_{\tilde{\chi}^{\pm}_1}$ and $\Delta m_{21} \sim 20$ GeV. This constitutes the first explanation of the soft-lepton excesses in a model with GUT relations among the soft SUSY-breaking parameters.