Boosting Higgs pair production in the $b\bar{b}b\bar{b}$ final state with multivariate techniques

TL;DR

This study evaluates the feasibility of measuring Higgs pair production in the $b\bar{b}b\bar{b}$ final state at the LHC by blending cut-based selections with advanced multivariate techniques. It models signal via gluon-fusion $hh$ production with full top-quark loop effects and includes irreducible $4b$ as well as reducible backgrounds from misidentified light/charm jets, assessing robustness to high pileup with pileup-mitigation strategies. The multivariate analysis using deep neural networks dramatically enhances sensitivity, achieving $S/\sqrt{B}\approx 4.0$ for $\mathcal{L}=3$ ab$^{-1}$ in the no-PU scenario and maintaining strong significance under PU conditions, indicating potential HL-LHC observation in this channel. The work highlights the importance of reducing mistag rates and improving mass resolution and PU treatment, and outlines paths toward constraining the Higgs trilinear coupling and probing BSM effects through di-Higgs kinematics.

Abstract

The measurement of Higgs pair production will be a cornerstone of the LHC program in the coming years. Double Higgs production provides a crucial window upon the mechanism of electroweak symmetry breaking and has a unique sensitivity to the Higgs trilinear coupling. We study the feasibility of a measurement of Higgs pair production in the $b\bar{b}b\bar{b}$ final state at the LHC. Our analysis is based on a combination of traditional cut-based methods with state-of-the-art multivariate techniques. We account for all relevant backgrounds, including the contributions from light and charm jet mis-identification, which are ultimately comparable in size to the irreducible $4b$ QCD background. We demonstrate the robustness of our analysis strategy in a high pileup environment. For an integrated luminosity of $\mathcal{L}=3$ ab$^{-1}$, a signal significance of $S/\sqrt{B}\simeq 3$ is obtained, indicating that the $b\bar{b}b\bar{b}$ final state alone could allow for the observation of double Higgs production at the High-Luminosity LHC.

Figures (22)

• Figure 1: Representative Feynman diagrams for Higgs pair production in gluon fusion at leading order. Only the fermion triangle loop diagram (right) is directly sensitive to the Higgs trilinear coupling $\lambda$. In the SM, the fermion loops are dominated by the contribution from the top quark.
• Figure 2: Comparison of the $p_T$ distributions of the leading (left) and subleading (right) large-$R$ jets in the boosted category, for signal and background events. Distributions have been normalized to unity. The total background is the sum of all components listed in Table \ref{['tab:samples']}.
• Figure 3: Same as Fig. \ref{['fig:cutplots1']} for the leading (left) and subleading (right) AKT03 subjets in the subleading Higgs candidate large-$R$ jet.
• Figure 4: Same as Fig. \ref{['fig:cutplots1']}, now for the $p_T$ and rapidity distributions of the small-$R$ jets corresponding to the resolved selection.
• Figure 5: Same as Fig. \ref{['fig:cutplots1']} for the invariant mass distribution of the leading Higgs candidates in the resolved (left) and boosted (right) selections.