Search for Light Scalars in the Two Real Singlet Model at the LHC

Abstract

We investigate exotic scalar decays $h_2 \to h_1 h_1$ in the Two Real Singlet Model (TRSM), focusing on light CP-even scalars with $20 \le M_{1} \le 60$~GeV and $20 \le M_{2} \le 120$~GeV. Unlike previous studies focused on gluon--gluon fusion or vector-boson fusion production, we explore associated production with electroweak gauge bosons, $pp \to Vh_2$ {\sl($V = W,Z$)}, as a complementary and experimentally clean probe of light scalar cascades in the TRSM. The subsequent decay $h_1 \to b\bar{b}$ leads to final states containing four $b$-jets accompanied by a charged lepton and missing transverse energy. We evaluate the sensitivity of the $4b+\ell\nu_\ell$ channel at $\sqrt{s}=13.6$~\TeV for the LHC Run~3 and the HL-LHC. For an integrated luminosity of $300~\mathrm{fb}^{-1}$, the $W^+h_2$ channel provides the strongest sensitivity, reaching a significance of approximately $4\sigma$, while the $W^-h_2$ channel reaches approximately $3\sigma$. At the HL-LHC with $3000~\mathrm{fb}^{-1}$, the corresponding significances increase to approximately $12\sigma$ and $8\sigma$, respectively, highlighting the strong discovery potential of associated light-scalar production in the TRSM.