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Probing gluons-enriched dark jets from Higgs boson exotic decays at the LHC

Wanyun Chen, Chih-Ting Lu, Hanxin Shen

Abstract

The dark sector may possess a rich structure yet to be uncovered, and a QCD-like dark sector with GeV-scale dark hadrons can yield novel signatures at the Large Hadron Collider (LHC). In this work, we focus on a light singlet pseudoscalar mediator that connects the QCD-like dark sector to the Standard Model (SM) sector via the Higgs portal. Notably, when the lightest unstable dark meson has a mass of approximately $3$ GeV, it predominantly decays into a pair of gluons and behaves as a long-lived particle, a scenario that has received relatively little attention. We consider various Higgs production channels at the LHC and investigate two processes for generating dark mesons: (1) the cascade decay of the Higgs boson into a pair of light pseudoscalar mediators, which subsequently decay into four dark mesons; and (2) the dark shower and hadronization process whereby the Higgs boson decays into a pair of dark quarks that subsequently evolve into dark mesons. These processes give rise to novel gluon-rich dark jets composed of long-lived dark mesons. Notably, we find that appropriate trigger selection constitutes a crucial factor for detecting these signal signatures in both tracker system and CMS muon system. At the high-luminosity LHC, the exotic Higgs branching ratio to cascade decays (dark showers) can be constrained below $\mathcal{O}(10^{-5}-10^{-1})$ [$\mathcal{O}(10^{-5}-10^{-2})$] for dark meson proper lifetimes $cτ$ ranging from $1$ mm to $100$ m.

Probing gluons-enriched dark jets from Higgs boson exotic decays at the LHC

Abstract

The dark sector may possess a rich structure yet to be uncovered, and a QCD-like dark sector with GeV-scale dark hadrons can yield novel signatures at the Large Hadron Collider (LHC). In this work, we focus on a light singlet pseudoscalar mediator that connects the QCD-like dark sector to the Standard Model (SM) sector via the Higgs portal. Notably, when the lightest unstable dark meson has a mass of approximately GeV, it predominantly decays into a pair of gluons and behaves as a long-lived particle, a scenario that has received relatively little attention. We consider various Higgs production channels at the LHC and investigate two processes for generating dark mesons: (1) the cascade decay of the Higgs boson into a pair of light pseudoscalar mediators, which subsequently decay into four dark mesons; and (2) the dark shower and hadronization process whereby the Higgs boson decays into a pair of dark quarks that subsequently evolve into dark mesons. These processes give rise to novel gluon-rich dark jets composed of long-lived dark mesons. Notably, we find that appropriate trigger selection constitutes a crucial factor for detecting these signal signatures in both tracker system and CMS muon system. At the high-luminosity LHC, the exotic Higgs branching ratio to cascade decays (dark showers) can be constrained below [] for dark meson proper lifetimes ranging from mm to m.
Paper Structure (11 sections, 24 equations, 23 figures, 3 tables)

This paper contains 11 sections, 24 equations, 23 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Higgs portal to dark QCD sector
  3. Constraints and benchmark points
  4. Exploring gluons-enriched dark jets at the LHC
  5. Emerging jet signatures in the tracker system
  6. Displaced shower signatures in the CMS muon system
  7. Numerical results and discussions
  8. Conclusion
  9. Kinematic analysis of the cascade decay scenario
  10. Supplementary results with R strategy in the EJ analysis
  11. $\Delta\phi(\vec{p}_T^{\,\text{miss}},\,\text{cluster})$ and $\Delta R(\text{jet, cluster})$ distributions for each Higgs production mode

Figures (23)

  • Figure 1: Efficiencies for the six major Higgs production processes (ggH, VBF, VH-had, VH-lep, $t\bar{t}H$-had & $t\bar{t}H$-semi, and $t\bar{t}H$-lep & $t\bar{t}H$-semi) under individual trigger conditions at the $\sqrt{s} = 14$ TeV HL-LHC.
  • Figure 2: Efficiencies for the six major Higgs production processes (ggH, VBF, VH-had, VH-lep, $t\bar{t}H$-had & $t\bar{t}H$-semi, and $t\bar{t}H$-lep & $t\bar{t}H$-semi) under combined trigger conditions of Categories I and II at the $\sqrt{s} = 14$ TeV HL-LHC.
  • Figure 3: Normalized distributions of the event-level median impact parameter $\langle IP_{2D} \rangle_{\text{event}}$ (left) and the $\alpha_{3D}$ calculated with $D_{\text{cut}}=10$ (right). The five signal BPs in the ggH production mode are distinguished by color: Dark shower scenarios DS1 (red), DS2 (blue), DS3 (green), and cascade decay scenarios cascade-1 (purple), cascade-2 (yellow). All BPs correspond to a fixed $c\tau_{\eta_d} = 25$ mm. The SM QCD light-jet background is shown as the grey dashed line CMS:2018bvr.
  • Figure 4: Multiplicity distributions of $\eta_d$'s (left) and reconstructed tracks (right) within the EJ cone ($R=0.4$). The distributions are obtained for EJ candidates in signal events in the ggH production mode and passing the trigger $H_T > 900$ GeV. The five signal BPs are distinguished by color: Dark shower scenarios DS1 (red), DS2 (blue), DS3 (green), and cascade decay scenarios cascade-1 (purple), cascade-2 (yellow). All BPs correspond to a fixed $c\tau_{\eta_d} = 25$ mm.
  • Figure 5: Maximum signal acceptance $A_{i,\text{max}}$ among the seven selection sets (left) and corresponding expected signal yield $N_S$ for $\mathcal{L}=16.1~\mathrm{fb}^{-1}$ (right) shown as a function of $c\tau_{\eta_d}$ for the DS1. The results are shown for Higgs production through ggH (purple), VBF (orange), VH-had (green), $t\bar{t}H$-had & $t\bar{t}H$-semi (blue), VH-lep (brown), and $t\bar{t}H$-lep (red).
  • ...and 18 more figures