Single Production of a Vector-Like Top as a Probe of Charged Higgs Bosons at a Muon-Proton Collider

TL;DR

This paper investigates the discovery prospects for a vector-like top partner ($T$) within the Type-II 2HDM (2HDM-II) at future high-energy $\mu p$ colliders. It focuses on the charged-Higgs mediated decay chain $T \to H^+ b$ with $H^+ \to tb$, leading to a distinctive final state of four $b$-jets plus a lepton and missing energy, explored through detector-level simulations. A parameter scan within the 2HDM-II+$TB$ framework shows that $T \to H^+ b$ dominates for $m_T > 1$ TeV, with four representative benchmarks around $m_T \approx 1.2$–$1.9$ TeV and $m_{H^\pm} \approx 600$–$650$ GeV. Using a Cowan-based significance with systematic uncertainties, the study finds discovery potential above $5\sigma$ at $\mathcal{L}=100$ fb$^{-1}$ for several benchmarks and $>10\sigma$ at $\mathcal{L}=234$ fb$^{-1}$ for the lighter points, illustrating strong sensitivity of a $\mu p$ collider to charged-Higgs sectors with VLQs.

Abstract

We investigate the discovery prospects for a vector-like top partner ($T$) within the Type-II Two-Higgs-Doublet Model (2HDM-II) at future high-energy $μp$ colliders. The analysis focuses on the charged Higgs decay mode $μ^+ p \to ν_μ\, \bar{b}T \to ν_μ\, \bar{b}H^+b$, with the subsequent decay $H^+\to t\bar{b}$ yielding a final state with multiple $b$-jets and a charged lepton. A detailed detector-level simulation is carried out for benchmark configurations with charged Higgs masses around 600-650~GeV and vector-like top masses in the range $m_T \simeq 1.0$-$1.8$~TeV. For an integrated luminosity of 100~fb$^{-1}$, discovery significances above $5σ$ are obtained across several benchmark points, remaining robust against systematic uncertainties up to 20\%. At higher luminosities of 234~fb$^{-1}$, the sensitivity exceeds $10σ$ for the lightest benchmarks and stays above $5σ$ even in the presence of 30\% systematics.

Figures (4)

• Figure 1: $\mathcal{BR}(T \to XY)$ as a function of $m_T$, with $XY = H^+ b$(teal green), $ht$(orange), $W^+ b$(violet), $Z t$(magenta), $A t$(green), and $H t$(golden yellow).
• Figure 2: Representative Feynman diagram for the single production of a VLT quark, followed by its decay into a charged Higgs boson and a bottom quark.
• Figure 3: Normalized distributions of $N[b]$, $p_T[b_1]$, $p_T[b_2]$, $p_T[b_3]$, $sp_T[b_1b_2b_3b_4]$, and $H_T$ for the four benchmark points and the SM backgrounds at $\sqrt{s}=9.16$ TeV.
• Figure 4: Discovery significance as a function of $m_T$ for different values of the systematic uncertainty $\delta$ and integrated luminosities $\mathcal{L}=100$ and $234$ fb$^{-1}$ at $\sqrt{s}=9.16$ TeV. The parameters are fixed to $m_{H^\pm}\simeq 600$ GeV with $m_H\simeq m_A\simeq m_{H^\pm}$, $\tan\beta = 5$, $s_R^u = 0.05$, and $s_R^d = 0.11$. All shown points satisfy the theoretical and experimental constraints discussed in the text.