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Probing Heavy Neutral Higgs Bosons via Single Vector-Like Bottom Quark Production at the HL-LHC

Rachid Benbrik, Mbark Berrouj, Mohammed Boukidi, Mohamed Ech-chaouy, Kholoud Kahime, Khawla Salime

Abstract

We investigate the discovery prospects of a singly produced vector-like bottom quark in the Type-II Two-Higgs-Doublet Model extended by an $SU(2)_L$ vector-like $(T,B)$ doublet. We focus on the non-standard decay chain $B \to φb$, followed by $φ\to t\bar{t}$, where $φ= H$ or $A$, leading to a final state with one charged lepton, missing transverse energy, and multiple $b$-jets. We perform a full simulation of both signal and Standard Model backgrounds at $\sqrt{s}=14$ TeV. We show that the exotic channels $B \to φb$ can dominate over the conventional decay modes, reaching branching ratios of order $50\%$ for both neutral scalars in the alignment limit. A conventional cut-based analysis provides a $5σ$ discovery significance only at sufficiently high integrated luminosity. By contrast, an XGBoost-based multivariate analysis substantially improves the signal-background discrimination and extends the discovery reach up to $m_B \simeq 1.3$ TeV with $600~\mathrm{fb}^{-1}$ and up to $m_B \simeq 1.6$ TeV with $3~\mathrm{ab}^{-1}$, even in the presence of systematic uncertainties as large as $15\%$.

Probing Heavy Neutral Higgs Bosons via Single Vector-Like Bottom Quark Production at the HL-LHC

Abstract

We investigate the discovery prospects of a singly produced vector-like bottom quark in the Type-II Two-Higgs-Doublet Model extended by an vector-like doublet. We focus on the non-standard decay chain , followed by , where or , leading to a final state with one charged lepton, missing transverse energy, and multiple -jets. We perform a full simulation of both signal and Standard Model backgrounds at TeV. We show that the exotic channels can dominate over the conventional decay modes, reaching branching ratios of order for both neutral scalars in the alignment limit. A conventional cut-based analysis provides a discovery significance only at sufficiently high integrated luminosity. By contrast, an XGBoost-based multivariate analysis substantially improves the signal-background discrimination and extends the discovery reach up to TeV with and up to TeV with , even in the presence of systematic uncertainties as large as .

Paper Structure

This paper contains 7 sections, 15 equations, 7 figures, 7 tables.

Table of Contents

  1. Introduction
  2. Theoretical framework
  3. Experimental and theoretical constraints
  4. Production and decay of vector-like bottom quarks
  5. Cut-based analysis
  6. Machine-learning analysis
  7. Conclusion

Figures (7)

  • Figure 1: Representative Feynman diagrams for single production of a vector-like bottom quark followed by the decay into a heavy neutral scalar $\phi$.
  • Figure 2: Left: leading-order $\sigma\left(pp \to \overline{B}b(B\overline{b})j\right)\times\mathrm{BR}\left(B(\overline{B}) \to \phi b(\overline{b})\right)$ with $\phi=H,A$ as a function of $m_B$. Right: corresponding branching ratios as functions of $m_B$, for $m_H=m_A=m_{H^\pm}=700$ GeV, $\tan\beta=6$, $s_R^u=0.01$, and $s_R^d=0.2$.
  • Figure 3: Normalized distributions of representative kinematic observables for the signal and the dominant SM backgrounds at $\sqrt{s}=14$ TeV.
  • Figure 4: ROC curves for BP1 (left), BP2 (center), and BP3 (right), showing the classifier performance on the training sample (yellow) and test sample (black).
  • Figure 5: BDT response distributions for the three benchmark points, comparing signal (blue) and background (red) in the training and testing samples. The legend shows the KS statistic and the corresponding $p$-value.
  • ...and 2 more figures