Semi-visible emerging jets

A bstract We propose a new class of dark-shower signatures in Standard Model extensions featuring Hidden Valleys or dark sectors coupled through an s-channel mediator. In this framework, unstable dark pions appear as long-lived particles (LLPs), with their lifetimes treated as free parameters. The resulting signatures, which we term semi-visible emerging jets (SVEJ), continuously interpolate between the established semi-visible and emerging jet regimes. We outline an analysis strategy optimized for dark pion lifetimes of order O(10) O 10 mm, and reinterpret existing LLP searches targeting lifetimes of O(100) O 100 – O(1000) O 1000 mm. Our proposed SVEJ search, exploiting the current ATLAS emerging-jet trigger, achieves sensitivity to cross sections of O(0.1) O 0.1 fb for lifetimes around O(10) O 10 mm. Finally, we advocate a more detailed study, including hadronisation uncertainties and detector-level effects.