Probing Extended Higgs Sectors via Multi-Top Events from Higgs Pair Decays in 2HDM Type-I at the HL-LHC

Abstract

This study investigates the production of multi-top quark events final states containing up to four top quarks as a probe for new physics beyond the Standard Model (SM) within the framework of the Two Higgs Doublet Model (2HDM) Type-I. Focusing on the High-Luminosity Large Hadron Collider (HL-LHC) at a center-of-mass energy of $\sqrt{s} = 14$TeV, we analyze associated production processes including $pp \to t\bar{t}H$, $pp \rightarrow t\bar{t}A$, $pp \rightarrow HA$, $pp \rightarrow HH^{\pm}$, and $pp \rightarrow AH^{\pm}$. The simulation pipeline incorporates theoretical constraints and branching ratios. By targeting these high-multiplicity final states, the research aims to establish the sensitivity of the HL-LHC to an extended Higgs sector, utilizing the top quark's unique coupling to the scalar field as a primary discovery channel. The analysis is centered on two benchmark points characterized by a degenerate mass spectrum ($m_H = m_A = m_{H^{\pm}} = 500$GeV) in the alignment limit ($\sin(\beta - \alpha) \to 1$), with $\tan\beta$ varied between 1 and 3. Event selection was performed with stringent cuts on jet multiplicity to suppress dominant SM backgrounds, such as $t\bar{t}W$, $t\bar{t}Z$, and $WWZ$. Our results indicate that signal significance improves substantially as the integrated luminosity increases from $3000~fb^{-1}$ to $4000~fb^{-1}$, with all investigated channels exceeding the $5\sigma$ discovery threshold.