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, $pp\to V{h}_2$ {\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.

Comments: 29 pages, 8 figures