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چکیده
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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 tt 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 com- pared 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[1]0 ) quasi-bound toponium state, as predicted by nonrelativistic quantum chromodynamics. Using a simplified model for 1S[1]0 to-ponium, the cross section of the excess above the pQCD prediction is measured to be 8.8 +1.2 −1.4 pb. .
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