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

TL;DR

The paper addresses the challenge of probing an extended Higgs sector within the 2HDM Type-I by leveraging high-multiplicity top-quark final states at the HL-LHC ($\\\sqrt{s}=14$ TeV). It deploys a full simulation chain (2HDMC constraints, MadGraph at LO, Pythia8, FastJet, MadAnalysis5) for five associated production channels with a degenerate heavy spectrum $m_H=m_A=m_{H^{\pm}}=500$ GeV in the alignment limit $\sin(\beta-\alpha)\to 1$, exploring two benchmark points with $\tan\beta=1$ and $3$. The analysis hinges on stringent jet and $b$-jet multiplicity cuts, exploiting a distinctive 12-jet, multi-top topology from $H/A\to t\bar{t}$ decays; results show that increasing the integrated luminosity from $3000$ to $4000$ fb$^{-1}$ dramatically enhances discovery potential, with all channels surpassing $5\sigma$ significance and the $AH^{\pm}$ channel achieving particularly high sensitivity. The study provides a concrete, top-quark–driven strategy for testing an extended Higgs sector at the HL-LHC and informs future experimental searches and parameter-space constraints.

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 ($\sin(β- α) \to 1$), with $\tanβ$ 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 $5σ$ discovery threshold.

Figures (9)

• Figure 1: Feynman diagram for the associated production of a heavy CP-even Higgs boson with a top-quark pair ($pp \to t\bar{t}H$) in the 2HDM Type-I, illustrating the decay chain leading to a 12-jet final state at the HL-LHC.
• Figure 2: Distribution of the transverse momentum ($p_T$) of jets for signal processes $pp \to t\bar{t}H$ and $pp \to t\bar{t}A$ compared against Standard Model background processes ($t\bar{t}W$, $t\bar{t}Z$, and $WWZ$) at $\sqrt{s} = 14$ TeV.
• Figure 3: Distribution of the transverse momentum ($p_T$) of jets for the signal process $pp \to AH^{\pm}$ along with Standard Model background processes, highlighting the harder $p_T$ spectrum of the BSM signal.
• Figure 4: Pseudorapidity ($\eta$) distribution of reconstructed jets for the signal processes $pp \to t\bar{t}H$ and $pp \to t\bar{t}A$ and relevant Standard Model backgrounds, illustrating the central nature of the signal jets.
• Figure 5: Pseudorapidity ($\eta$) distribution of jets for the $pp \to AH^{\pm}$ signal process alongside Standard Model background processes at 14 TeV center-of-mass energy.