Abstract A search for resonances in top quark pair (tt) production in final states with two charged leptons and multiple jets is presented, based on proton-proton collision data collected by the CMS experiment at the CERN LHC at s = 13 TeV, corresponding to 138 fb^-1. The analysis explores the invariant mass of the system and two angular observables that provide direct access to the correlation of top quark and antiquark spins. A significant excess of events is observed near the kinematic tt threshold compared to the nonresonant production predicted by fixed-order perturbative quantum chromodynamics (pQCD). The observed enhancement is consistent with the production of a color-singlet pseudoscalar (¹S^1₀) quasi-bound toponium state, as predicted by nonrelativistic quantum chromodynamics. Using a simplified model for ¹S^1₀ toponium, the cross section of the excess above the pQCD prediction is measured to be 8. 8^+1. 2-₁. ₄ pb.
G. Alverson (Tue,) studied this question.