Statistical Indications of Toponium Formation in Top Quark Pair Production

We present an analysis of six differential cross-section measurements of top-quark pair production in the dilepton channel from the ATLAS and CMS experiments. The data are compared to state-of-the-art QCD predictions with and without the inclusion of toponium formation effects. This contribution is modelled via a re-weighting of fixed-order matrix elements using the Green’s function of the non-relativistic QCD Hamiltonian, and we employ a statistical model to quantify the preference of the data for the toponium hypothesis. All observables yield Bayes factors larger than unity, with two exceeding 20, yielding strong evidence for the toponium hypothesis in top-quark pair production at the LHC.

💡 Research Summary

The authors investigate whether non‑relativistic bound‑state effects, commonly referred to as “toponium,” manifest in top‑quark pair production at the LHC. They select six particle‑level differential cross‑section measurements in the dilepton channel—one two‑dimensional distribution (the invariant mass of the dilepton system mℓℓ versus the azimuthal separation Δφℓℓ) and five one‑dimensional distributions (mℓℓ, Δφℓℓ, and Δηℓℓ from ATLAS and CMS). All observables are normalised to unit area to maximise sensitivity to shape distortions while suppressing overall normalisation uncertainties.

The theoretical baseline (null hypothesis H₀) consists of state‑of‑the‑art NNLO QCD predictions (including NLO electroweak corrections and threshold resummation) obtained with NNPDF3.1 PDFs. The alternative hypothesis H₁ adds a toponium contribution obtained by re‑weighting the leading‑order gg→bℓνℓ b̄ℓ′νℓ′ matrix element with the Green’s function of the non‑relativistic QCD Hamiltonian, as described in Ref.