Higgs Boson Production in Association with a Single Top Quark as a Probe of the Top Yukawa Coupling

Abstract

This paper provides a detailed analysis of the associated production of the Higgs boson with a single top quark ($tH$) in proton-proton collisions at $\sqrt{s} = 13~\mathrm{TeV}$ and $14~\mathrm{TeV}$. Based on the ATLAS search, we have employed innovative modeling approaches to improve the sensitivity to new physics and improve Standard Model constraints. The major goals are to optimize the data selection, statistical error estimation, determination of physical limits on the top quark Yukawa coupling ($κ_t$), and future experimental projections for HL-LHC. Simulations with MadGraph5aMC@NLO at LO+MLM give cross-sections of $σ_{tHq}$ and $σ_{tWh}$ in SM, scaled by K-factors to simulate NLO accuracy. For inverted $κ_t = -1$ (ITC), positive enhancements are seen, consistent with constructive interference. Kinematic distributions ($H_T$, $p_T(h)$, $η[j]$, $ΔR[t,h]$) are checked against ATLAS expectations, confirming the optimized approach to maximize signal extraction and suppress systematics.

Figures (9)

• Figure 1: Representative dominant leading-order Feynman diagrams in the 4FS: (left) $tHq$ production via $t$-channel-like exchange and (right) $tWH$ production via gluon $b$ interaction with time-like virtual top quark mediator and Higgs radiation, atlas_tH_2025
• Figure 2: $H_T$ distribution for simulated tHq events from LO+MLM simulations at $\sqrt{s}=13$ TeV.
• Figure 3: Transverse momentum distribution of the Higgs boson, $p_T(h)$, in GeV/c for simulated $tHq$ events in the inverted Yukawa coupling scenario ($\kappa_t = -1$) at $\sqrt{s}=13$ TeV (LO+MLM). The steeply falling spectrum is consistent with ATLAS post-fit shapes and the expected $t$-channel kinematics, with moderate $p_T(h)$ dominated by top/forward-jet recoil.
• Figure 4: Distribution of the pseudorapidity $\eta_j$ of the forward light-quark jet in simulated $tHq$ events.
• Figure 5: Distribution of the angular separation $\Delta R(p_j, h)$ between the forward light-quark jet and the Higgs boson in simulated $tHq$ events under the inverted Yukawa coupling scenario ($\kappa_t = -1$) at $\sqrt{s}=13$ TeV (LO+MLM). The peak at $\Delta R \approx 3$--$4$ reflects the recoil of the forward jet against the central $tH$ system.