Abstract
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
$$ \mathcal{O}(10) $$
O
10
mm, and reinterpret existing LLP searches targeting lifetimes of
$$ \mathcal{O}(100) $$
O
100
–
$$ \mathcal{O}(1000) $$
O
1000
mm. Our proposed SVEJ search, exploiting the current ATLAS emerging-jet trigger, achieves sensitivity to cross sections of
$$ \mathcal{O}(0.1) $$
O
0.1
fb for lifetimes around
$$ \mathcal{O}(10) $$
O
10
mm. Finally, we advocate a more detailed study, including hadronisation uncertainties and detector-level effects.