Search for dark mesons decaying to top and bottom quarks in proton-proton collisions at √s = 13 TeV with the ATLAS detector

A search for dark mesons originating from strongly-coupled, SU(2) dark flavor symmetry conserving models and decaying gaugephobically to pure Standard Model final states containing top and bottom quarks is presented. The search targets fully hadronic final states and final states with exactly one electron or muon. The analyzed dataset corresponds to an integrated luminosity of 140 fb⁻¹ of proton-proton collisions collected at √s = 13 TeV with the ATLAS detector at the Large Hadron Collider. No significant excess over the Standard Model background expectation is observed and the results are used to set the first direct constraints on this type of model. The two-dimensional signal space of dark pion masses m_πD and dark rho-meson masses m_ρD is scanned. For m_πD/m_ρD = 0.45, dark pions with masses m_πD < 943 GeV are excluded, while for m_πD/m_ρD = 0.45 masses of m_πD < 738 GeV are excluded.