Extracting Higgs Self-Coupling Constraints through Triple Higgs Boson Production at Future Hadron Colliders

TL;DR

This study investigates how future hadron colliders can constrain Higgs self-interactions by examining triple-Higgs production in the six-$b$-jet final state. It employs both a traditional cut-based analysis and a gradient-boosting XGBoost approach, under realistic detector smearing and EFT truncation schemes, to extract constraints on the trilinear and quartic couplings via the EFT parameters $c_3$ and $d_4$. The results show that, with few-percent systematic uncertainties, meaningful and perturbativity-compatible bounds are achievable, with multivariate methods offering robustness and higher sensitivity; 85 TeV colliders provide comparable reach to 100 TeV machines. The work also analyzes the impact of detector effects, background normalization, and different EFT truncations, and demonstrates that the six-$b$ channel remains a viable probe when extrapolated to various collider energies and luminosities. Overall, the six-$b$ final state can play a crucial role in measuring Higgs self-interactions, particularly when complemented by other triple-Higgs channels in a global EFT framework.

Abstract

We present a systematic study of triple Higgs boson production at future high-energy hadron colliders, using the six-$b$-jet final state as a probe of the Higgs self-interactions. We conduct, under realistic detector smearing assumptions, both a traditional cut-based analysis, and a multivariate one using gradient boosting. The multivariate strategy is found to enhance sensitivity to beyond the Standard Model effects on the Higgs boson's self-couplings, while preserving large signal event yields, thus enabling more robust statistical inference. This allows us to assess the impact of detector effects, systematic uncertainties, background normalisation, as well as different truncation choices in an effective-field-theory description of the new physics effects possibly affecting the Higgs boson's self-interactions. Our results demonstrate that statistically-meaningful and perturbative-unitarity-compatible constraints on the trilinear and quartic Higgs boson self-couplings can be achieved, provided that systematic uncertainties are controlled at the few-percent level. Finally, we extrapolate our results to various collider energies and luminosities, demonstrating in particular that an 85 TeV proton-proton collider performs comparably to a 100 TeV machine. Altogether, our findings therefore establish the six-$b$ channel as a viable probe of the Higgs self-interactions at most future hadron collider options currently being examined by the high-energy physics community.

Figures (10)

• Figure 1: Regions of the $(c_3,d_4)$ parameter space where the $gg \to hhh$ cross section becomes negative under different truncation schemes: linear (green), quadratic (black) and cubic (blue). The non-truncated case remains positive definite for all values of $c_3$ and $d_4$.
• Figure 2: Impact of ATLAS-like and CMS-like jet smearing on the $\chi^{2,(6)}_\text{min}$ variable defined in section \ref{['sec:analysis']}, in the case of SM triple Higgs boson production.
• Figure 3: Comparison of the $2\sigma$ limits on the $(c_3,d_4)$ plane expected from $L=20$ ab$^{-1}$ of proton-proton collisions at $\sqrt{s}=100$ TeV, obtained with the cut-based analysis (dashed blue) and with the XGBoost approach (dotted black). Results are shown without smearing and systematics.
• Figure 4: Comparison of the $2\sigma$ limits on the $(c_3,d_4)$ plane expected from $L=20$ ab$^{-1}$ of proton-proton collisions at $\sqrt{s}=100$ TeV, obtained with the cut-based analysis (left) and the XGBoost analysis (right). Results are shown for the Monte Carlo truth (dotted black, no smearing) as well as for the considered ATLAS-like (dashed blue) and CMS-like (solid red) jet smearing models.
• Figure 5: Impact of the $b$-tagging efficiency on the $2\sigma$ reach in the $(c_3,d_4)$ plane, as expected from 20 ab$^{-1}$ of proton-proton collisions at $\sqrt{s}=100$ TeV. Contours are shown for CMS-like jet smearing functions within the XGBoost analysis, and correspond to $\mathcal{P}(b\!\rightarrow\! b)=80\%$ (dashed black), 85% (solid red) and 90% (dotted blue).