Search for Resonant Production of Dark Quarks in the Dijet Final State with the ATLAS Detector

This paper presents a search for a new $Z^{\mathrm{\prime }}$ resonance decaying into a pair of dark quarks which hadronise into dark hadrons before promptly decaying back as Standard Model particles. This analysis is based on proton-proton collision data recorded at $\sqrt{s}=13$ TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to an integrated luminosity of 139 fb${}^{-1}$. After selecting events containing large-radius jets with high track multiplicity, the invariant mass distribution of the two highest-transverse-momentum jets is scanned to look for an excess above a data-driven estimate of the Standard Model multijet background. No significant excess of events is observed and the results are thus used to set 95 % confidence-level upper limits on the production cross-section times branching ratio of the $Z^{\mathrm{\prime }}$ to dark quarks as a function of the $Z^{\mathrm{\prime }}$ mass for various dark-quark scenarios.