Anatomy of $tthh$ physics at the HL-LHC

Journal Article · 31 March 2020 · Physical Review. D.

DOI: https://doi.org/10.1103/physrevd.101.055043 · OSTI ID:1607819

Li, Lingfeng ^[1]; Li, Ying-Ying  ^[2]; Liu, Tao  ^[1]

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1. The Hong Kong Univ. of Science and Technology (Hong Kong)
2. The Hong Kong Univ. of Science and Technology (Hong Kong); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

The $tthh$ production at colliders contains rich information on the nature of the Higgs boson. In this article, we systematically studied its physics at the high-luminosity Large Hadron Collider (HL-LHC), using exclusive channels with multiple ( $\ge 5$) $b$-jets and one lepton ( $5b1\ell$), multiple ( $\ge 5$) $b$-jets and opposite-sign dilepton ( $5b2\ell$), same-sign dilepton ( $\mathrm{SS}2\ell$), multiple leptons (multi- $\ell$), and ditau resonance ( $\tau \tau$). The scenarios analyzed include: (1) the $tthh$ production in Standard Model; (2) the $tthh$ production mediated by anomalous cubic Higgs self-coupling and $tthh$ contact interaction; (3) heavy Higgs ( $H$) production with $ttH\to tthh$; and (4) pair production of fermionic top partners ( $T$) with $TT\to tthh$. To address the complication of event topologies and the mess of combinatorial backgrounds, a tool of boosted-decision-tree was applied in the analyses. The $5b1\ell$ and $\mathrm{SS}2\ell$ analyses define the two most promising channels. For the nonresonant $tthh$ production, a combination of these exclusive analyses allows for its measurement in the SM with a statistical significance $~0.9\sigma$ (with $S/B>1\%$), and may partially break the sensitivity degeneracy with respect to a varying cubic Higgs self-coupling, a difficulty usually thought to exist in gluon fusion di-Higgs analysis at HL-LHC. These sensitivities were also projected to future hadron colliders at 27 TeV and 100 TeV. For the resonant $tthh$ productions, the heavy Higgs boson in type II two-Higgs-doublet-model could be efficiently searched for between the mass thresholds $2m_h<m_H<2m_t$ and even beyond that, for relatively small $\tan \beta$ (vacuum alignment), while the fermionic top partners in composite Higgs models could be probed up to $~1.5\mathrm{TeV}$ and $~1.7\mathrm{TeV}$, for $\mathrm{Br}(T\to th)=25\%$ and 50%, respectively.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP); Research Grants Council (RGC)
• Grant/Contract Number: AC02-07CH11359; 16312716
• OSTI ID: 1607819
• Alternate ID(s): OSTI ID: 1638684
• Report Number(s): arXiv:1905.03772; FERMILAB-PUB-19-721-T; oai:inspirehep.net:1734003; TRN: US2201809
• Journal Information: Physical Review. D., Vol. 101, Issue 5; ISSN 2470-0010
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English