Abstract
We assess the current coverage and the future discovery potential of LHC searches for heavy Higgs bosons decaying into long-lived particles (LLPs), focusing primarily on the production of pairs of LLPs with hadronic final states. These signatures are generic in dark sectors where a heavy scalar decays into pairs of lighter states which subsequently mix with the Standard Model Higgs. We show that a handful of existing analyses provide broad coverage of LLP decay lengths ranging from millimeters to tens of meters, and explore the complementarity between searches for displaced and prompt final states in several simplified models. For both heavy singlet and heavy doublet scalars, LLP searches typically provide the leading sensitivity in current data and exhibit the strongest discovery potential in future LHC runs. We further translate the impact of these searches into the parameter space of various Twin Higgs models, demonstrating that LLP searches are a promising avenue for discovering a Twin Higgs with displaced decays. Finally, we propose a variety of additional search channels that would improve coverage of the second Higgs at the lifetime frontier.
Highlights
Considerably less attention has been devoted to potential exotic decays of additional Higgs bosons, in which the final states are quite unlike those expected from the direct couplings of new Higgs states to Standard Model particles
Far from being an exclusive property of isolated models, such exotic decay modes are a generic feature of theories that extend more than just the Higgs sector of the Standard Model
The search for additional Higgs bosons is a crucial component of the physics program at the Large Hadron Collider
Summary
We begin by exploring the phenomenology of a second Higgs-like scalar with potentially exotic decays in a relatively model-independent fashion. We focus primarily on the case of a CP-even neutral scalar, which may be an isolated state or a component of a larger electroweak multiplet Such a scalar resonance φ could have nonzero branching ratios directly into Standard Model states as well as into new states in a “dark” sector. Hadronic final states in these channels would lead to bounds qualitatively similar to those obtained from LLP decays into b quarks Another two parameters of central importance are the mass mX of the dark sector state and its total decay width ΓX into SM states ( assuming, for simplicity, that X decays exclusively into the SM). For completeness we present our results on displaced searches at 8 TeV in appendix A
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