  In this work, we propose a novel search strategy for new physics at the LHC
that utilizes calorimeter jets that (i) are composed dominantly of displaced
tracks and (ii) have many different vertices within the jet cone. Such emerging
jet signatures are smoking guns for models with a composite dark sector where a
parton shower in the dark sector is followed by displaced decays of dark pions
back to SM jets. No current LHC searches are sensitive to this type of
phenomenology. We perform a detailed simulation for a benchmark signal with two
regular and two emerging jets, and present and implement strategies to suppress
QCD backgrounds by up to six orders of magnitude. At the 14 TeV LHC, this
signature can be probed with mediator masses as large as 1.5 TeV for a range of
dark pion lifetimes, and the reach is increased further at the high-luminosity
LHC. The emerging jet search is also sensitive to a broad class of long-lived
phenomena, and we show this for a supersymmetric model with R-parity violation.
Possibilities for discovery at LHCb are also discussed.
