# The second Higgs at the lifetime frontier

## TL;DR

This paper evaluates the current and future potential of LHC searches for heavy Higgs bosons decaying into long-lived particles, highlighting the importance of LLP searches in discovering new physics such as Twin Higgs models.

## Contribution

It provides a comprehensive analysis of LLP search coverage, compares displaced and prompt decay searches, and proposes new channels to enhance discovery prospects for the second Higgs.

## Key findings

- LLP searches currently provide broad coverage for decay lengths from millimeters to tens of meters.
- LLP searches often outperform prompt decay searches in sensitivity for heavy scalars.
- Proposed new search channels could significantly improve the discovery potential of the second Higgs.

## 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.