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Observation of a pseudoscalar excess at the top quark pair production threshold

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arxiv 2503.22382 v2 pith:M56T3UBP submitted 2025-03-28 hep-ex

Observation of a pseudoscalar excess at the top quark pair production threshold

classification hep-ex
keywords textproductionexcessquarkchromodynamicsobservedpairpqcd
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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A search for resonances in top quark pair ($\text{t}\bar{\text{t}}$) 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 $\sqrt{s}$ = 13 TeV, corresponding to 138 fb$^{-1}$. The analysis explores the invariant mass of the $\text{t}\bar{\text{t}}$ 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 $\text{t}\bar{\text{t}}$ 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 ($^1$S$^{[1]}_0$) quasi-bound toponium state, as predicted by nonrelativistic quantum chromodynamics. Using a simplified model for $^1$S$^{[1]}_0$ toponium, 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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Cited by 23 Pith papers

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