Unveiling E$_6$SSM Scalar Diquarks at the HL-LHC

Abstract: We investigate the phenomenology of scalar diquarks with sub-TeV masses within the framework of the $E_6$ Supersymmetric Standard Model (E$_6$SSM) at the Large Hadron Collider (LHC). Focusing on the lightest of the six diquarks predicted by the model, we select some representative low masses for them in a parameter space region consistent with experimental constraints from direct searches for additional Higgs boson(s), Cold Dark Matter (CDM), and supersymmetry, as well as from flavor physics analyses. Using Monte Carlo ($MC$) simulations, we assess these benchmark points against the latest LHC results corresponding to an integrated luminosity of 140 fb$<sup>{-1}$. We further evaluate the signal significance of the pair-production of these diquarks, when each of them decays into $tb$ pairs, at the $\sqrt{s}=13$ TeV LHC Run 3 with design integrated luminosity of 300 fb$<sup>{-1}$, and also at the 3000 fb$<sup>{-1}$ High-Luminosity LHC (HL-LHC). Our analysis yields a statistical significance exceeding $3\sigma$ at the HL-LHC for diquark masses up to 1 TeV, indicating promising prospects for their discovery.