Higgs self-coupling measurements at the LHC

TL;DR

This work analyzes how to measure the Higgs self-coupling $\lambda$ at the LHC for a SM-like Higgs around $m_h=125$ GeV by studying dihiggs production in multiple channels and kinematic regimes. It emphasizes full one-loop calculations for $gg\to hh$ (beyond EFT) and investigates both inclusive $hh$ and $hh+j$ production, employing boosted techniques and jet-substructure to enhance sensitivity, particularly in $h\to b\bar{b}, W^+W^-, \tau^+\tau^-$ final states. The study finds inclusive channels suffer from large backgrounds, while boosted channels—especially $hh\to b\bar{b}\tau^+\tau^-$ and $hhj\to b\bar{b}\tau^+\tau^- j$—offer the most promise, given sufficient luminosity and robust $\tau$ tagging. Overall, a combination of channels and jet-assisted strategies could enable meaningful constraints on $\lambda$ at the LHC, highlighting the importance of high-luminosity data and advanced reconstruction techniques.

Abstract

Both the ATLAS and CMS collaborations have reported a Standard Model Higgs-like excess at around $m_h = 125$ GeV. If an SM-like Higgs particle is discovered in this particular mass range, an important additional test of the SM electroweak symmetry breaking sector is the measurement of the Higgs self-interactions. We investigate the prospects of measuring the Higgs self-coupling for $m_h=125 \gev$ in the dominant SM decay channels in boosted and unboosted kinematical regimes. We further enhance sensitivity by considering dihiggs systems recoiling against a hard jet. This configuration exhibits a large sensitivity to the Higgs self-coupling which can be accessed in subjet-based analyses. Combining our analyses allows constraints to be set on the Higgs self-coupling at the LHC.

Figures (8)

• Figure 1: Sample Feynman graphs contributing to $pp\to hh+X$. Graphs of type (a) yield vanishing contributions due to color conservation.
• Figure 2: Comparison of the (normalized) $p_{T,h}$ distributions in $pp\to hh+X$ at LO for different multiples of the trilinear Higgs coupling $\lambda$ ($m_t=172.5~{\rm{GeV}}$ and $m_b=4.5~{\rm{GeV}}$ using CTEQ6l1 parton densities).
• Figure 3: Comparison of $pp\to hh+X$ at LO. We choose $m_t=175~{\rm{GeV}}$ as in Ref. Plehn:1996wb, from which we also obtain the dashed blue reference line, and $m_b=4.5~{\rm{GeV}}$ and we use the CTEQ6l1 parton distributions.
• Figure 4: Sample Feynman graphs contributing to $pp \to hh+j+X$. Not shown are the $qg,\bar{q} g$ and $q\bar{q}$ subprocesses.
• Figure 5: Comparison of the leading order $p_{T,j}$ spectrum for $pp\to hh+j+X$ production. Shown are distributions for the effective interaction (obtained with MadGraph v5 Alwall:2011uj via FeynRulesChristensen:2008py and UfoDegrande:2011ua), and the full one-loop matrix element calculation. We again choose $m_t=172.5~{\rm{GeV}}$ and $m_b=4.5~{\rm{GeV}}$ using CTEQ6l1 parton densities and $\mu_F=\mu_R=p_{T,j}+2m_h$.