Standard Model Higgs boson pair production in the $(b\bar{b})(b\bar{b})$ final state

TL;DR

This study investigates constraining the Higgs self-coupling $λ$ via Higgs pair production in the all-hadronic final state $hh \to (bb)(bb)$ at the HL-LHC. It leverages boosted regimes and jet-substructure techniques (BDRS and Shower Deconstruction) to suppress daunting QCD and EW backgrounds and quantifies the sensitivity across integrated luminosities. The main result is that, with 3000 fb^-1 at 14 TeV, a 95% CL limit $λ ≤ 1.2 λ_{SM}$ is achievable under statistical uncertainties, with a data-driven side-band approach proposed to further control backgrounds. The work highlights the need for improved triggering and $b$-tagging to fully exploit this channel and calls for experimental follow-up to validate and extend these findings.

Abstract

Measuring the Higgs boson couplings as precisely as possible is one of the major goals of the High Luminosity LHC. We show that the $(b\bar{b})(b\bar{b})$ final state in Higgs boson pair production can be exploited in the boosted regime to give constraints on the trilinear Higgs boson self-coupling. In these exclusive phase space regions, novel jet substructure techniques can be used to separate the signal from the large QCD and electroweak backgrounds. New developments on trigger and b-tagging strategies for the upcoming LHC runs are necessary in order to reconstruct the Higgs bosons in boosted final states, where the trilinear self-coupling sensitivity is reduced. We find that using our approach one can set a limit for $λ\leq 1.2$ at $95 \%$ CL after $3000~\mathrm{fb}^{-1}$. As the signal-to-background ratio is small we propose a data-driven side-band analysis to improve on the coupling measurement.

Figures (9)

• Figure 1: Higgs boson pair production diagrams contributing to the gluon fusion process at LO are shown for a fermion $f$. These are generic diagrams and therefore, do not include all permutations.
• Figure 2: The transverse momentum of a Higgs boson in the pair production process, including the box and triangle diagrams as well as their interference, for several values of the self-coupling, given as multiples of the SM value.
• Figure 3: The transverse momentum of the four leading anti-$k_t$$R=0.4$ b-jets in the SM $hh\rightarrow (b\bar{b}) (b\bar{b})$ signal, before any cuts (left) and after the basic cuts as described in Section \ref{['sec:basic']} (right).
• Figure 4: The black curve shows the total NLO cross section at a 14 TeV LHC calculated for each value of $\lambda$ using the HPAIR program, not including the branching ratio for $hh \rightarrow (b\bar{b})(b\bar{b})$. The blue dashed curve shows the resulting cross section after the 'basic' analysis is applied to each signal sample, including the branching ratio for the $hh$ decays.
• Figure 5: The difference in rapidity between the two leading $R=1.2$ Cambridge-Aachen jets for the backgrounds and the $\lambda = \lambda_{SM}$ signal.