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 $SU(2{)}_L$ vector-like $(T,B)$ doublet. We focus on the non-standard decay chain $B\to \varphi b$, followed by $\varphi \to t\bar{t}$, where $\varphi =H$ 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 $B\to \varphi b$ 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 $5\sigma$ 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 $15\%$.