QCD at the Extremes

Session

Onium production: Toponium and other Onia

5 Sept 2025, 13:40

63. Intro

Alexander Grohsjean (Hamburg University (DE))

05/09/2025, 13:45

1. Quarkonium Parton Shower in Herwig 7

Aidin Masouminia (IPPP, Durham University)

05/09/2025, 14:00

I will present the implementation of a fully automated quarkonium parton shower in Herwig 7, based on NRQCD factorisation with spin–colour projections. The framework systematically includes both colour-singlet and colour-octet production mechanisms, as well as gluon fragmentation and diquark production processes. Perturbative short-distance coefficients are combined with non-perturbative NRQCD...

32. On the threshold behaviour of heavy top production

Torbjorn Sjostrand (Lund University (SE))

05/09/2025, 14:25

Back in 1990 an article by Victor Fadin. Valery Khoze and the speaker studied the effects of Coulomb enhancements and pseudo-bound below-threshold contributions ("toponium").
The relevant formulae have now been recoded and made available as an add-on to Pythia8, both for singlet and octet states.
Cross sections can be explored under varying assumptions. Complete events can be generated, but...

31. Observation of a cross-section enhancement near the $t\bar{t}$ production threshold in $\sqrt{s}=$13 TeV $pp$ collisions with the ATLAS detector

Baptiste Ravina (CERN)

05/09/2025, 14:50

I will present the recent ATLAS result on the observation of an excess near the $t\bar{t}$ threshold that is consistent with the formation of "toponium" quasi-bound states. Details of the experimental and statistical analysis techniques will be presented, with an emphasis on the modelling of both pQCD and pNRQCD $t\bar{t}$ production.

42. Toponium modelling at the LHC: from toy models to NRQCD predictions

Benjamin Fuks

05/09/2025, 15:20

We present recent developments in the description of toponium production at the LHC. Building upon a dedicated NRQCD framework, we compare predictions obtained with Green's function re-weighting to those originating from simplified pseudo-scalar models, including both narrow-width and broad-width setups. Using event generation with a consistent toolchain, we illustrate how these approaches...

57. Updated predictions for toponium production at the LHC

Sven-Olaf Moch, Sven-Olaf Moch (Hamburg University (DE))

05/09/2025, 15:45

We provide an update on QCD predictions for top-quark pair production close to threshold, including bound state effects at the Large Hadron Collider. We compute the top-quark pair invariant mass distribution, including Coulomb resummation for bound-state effects, as well as threshold resummation for emissions of soft and collinear gluons. We discuss uncertainty estimates and present a proposal...

33. How well does NRQCD describe quarkonium production data?

Mathias Butenschoen

05/09/2025, 16:10

We perform a thorough investigation of the universality of the long distance matrix elements (LDMEs) of nonrelativistic QCD factorization based on a next-to-leading order (NLO) fit of $J/\psi$ color octet (CO) LDMEs to high transverse momentum $p_T$ $J/\psi$ and $\eta_c$ production data at the LHC. We thereby apply a novel fit-and-predict procedure to systematically take into account scale...

58. General Discussion

05/09/2025, 16:35