Di-Higgs final states augMT2ed -- selecting $hh$ events at the high luminosity LHC

TL;DR

The paper tackles measuring the Higgs self-coupling via di-Higgs production at the LHC, focusing on the hh -> bb tau+ tau- final state where ttbar backgrounds are formidable. It advocates using kinematic bounding variables, especially m_T2, in combination with jet- and tau-related mass constraints to suppress backgrounds and enable a realistic HL-LHC sensitivity study. A detector-level analysis with HL-LHC assumptions shows that the di-Higgs cross section could be measured at about 30% precision, implying roughly 60% sensitivity to the Higgs trilinear coupling, with further gains possible through jet substructure and tau-tagging improvements. These findings demonstrate a viable path to probing the Higgs potential and guiding future experimental strategies at the HL-LHC.

Abstract

Higgs boson self-interactions can be investigated via di-Higgs ($pp\to hh+X$) production at the LHC. With a small ${\cal{O}}(30)$ fb Standard Model production cross section, and a large $t\bar t$ background, this measurement has been considered challenging, even at a luminosity-upgraded LHC. We demonstrate that by using simple kinematic bounding variables, of the sort already employed in existing LHC searches, the dominant $t\bar t$ background can be largely eliminated. Simulations of the signal and the dominant background demonstrate the prospect for measurement of the di-Higgs production cross section at the 30% level using 3/ab of integrated luminosity at a high-luminosity LHC. This corresponds to a Higgs self-coupling determination with 60% accuracy in the $b\bar b τ^+τ^-$ mode, with potential for further improvements from e.g. subjet technologies and from additional di-Higgs decay channels.

Figures (2)

• Figure 1: Transverse momentum distribution of the reconstructed Higgs (i.e. the $b\bar{b}$ pair) and the $m_{\text{T2}}$ distribution after the analysis steps described in the text have been carried out (see also Tab. \ref{['tab:bbtautau']}) but before cuts on either $m_{\text{T2}}$ or $p_{\text{T},b\bar{b}}$ have been applied.
• Figure 2: Luminosity in fb^-1$\mathrm{fb}^{-1}$ required to reach $S/\sqrt{B}=5$ for di-Higgs production based on simple rectangular cuts on $p{{\rm T},b\bar{b}}$p_ T,bb̅$$ and $m_{\rm T2}$m_ T2$$. Numbers in red show luminosities that would require a combination of the ATLAS and CMS data sets from a $3\,\mathrm^{-1}$ab^-1$$ high luminosity LHC.