Search for emerging jets in $pp$ collisions at √s = 13 TeV with the ATLAS experiment

A search is presented for emerging jets using 140~fb⁻¹ 140 fb - 1 of proton–proton collision data at √s = 13~TeV s = 13 TeV , collected by the ATLAS experiment between 2015 and 2018. The search looks for the existence of a dark sector with symmetries similar to those in quantum chromodynamics. This dark sector is populated with dark quarks, which undergo showering similar to quarks in the Standard Model, leading to a high multiplicity of long-lived dark hadrons within a dark jet. These dark hadrons subsequently decay to Standard Model particles via a new heavy scalar mediating particle φ ϕ . This results in jets which contain multiple displaced vertices, known as emerging jets. This analysis targets four-jet topologies, with two emerging jets and two Standard Model jets, resulting from the decay of pair-produced scalar mediators. No significant excess above the Standard Model background is observed. For dark pion proper decay lengths of 20~mm 20 mm , mediator masses are excluded between 1 and 2~TeV 2 TeV assuming a dark pion mass of 20~GeV 20 GeV .