A Search for Emerging Jets at $\sqrt{s}$ = 13 TeV at ATLAS Run 2

A search is presented for emerging jets, new exotic objects arising in models with QCD- like hidden sectors where dark quarks undergo dark showering, yielding long-lived dark hadrons that subsequently decay to visible jets with multiple small and varyingly-displaced vertices within the jet cone. Pair-production of a new scalar mediator that connects the two sectors and decays to a SM quark and a dark quark thus results in a four-jet final state of two QCD jets and two emerging jets. The search uses 139 fb$^{−1}$ of $\sqrt{s}$ = 13 TeV proton- proton collision data collected by the ATLAS experiment at the LHC during Run 2 in 2015-2018 and relies heavily on dedicated large-radius tracking and displaced-vertexing techniques, special reconstruction algorithms developed specifically for identifying long-lived particle signatures. The search probes emerging jets produced in the inner detector from dark scalar mediators with masses between $m$$_{xd}$ = 600 GeV and $m$$_{Xd}$ = 1400 GeV and dark pions with lifetimes between $CT$$_{\tau}$$_{d}$ = 0.5 mm and $CT$$_{\tau}$$_{d}$ = 300 mm.