| Title: |
Observation of a cross-section enhancement near the t̅t production threshold in √s=13 TeV pp collisions with the ATLAS detector |
| Authors: |
Collaboration, ATLAS |
| Publication Year: |
2026 |
| Collection: |
University of Glasgow: Enlighten - Publications |
| Description: |
A measurement of t̅t production is presented in the invariant-mass region near the pair production threshold, 𝑚ₜ-ₜ ∼ 345 GeV, in final states with two charged leptons and multiple jets. The measurement is based on 140 fb⁻¹ of proton–proton collision data collected at √𝑠 = 13 TeV with the ATLAS detector at the Large Hadron Collider. The data are compared to two models of t̅t production: a baseline model including only perturbative QCD predictions for the hard process, and an extended model that, in addition, incorporates non-relativistic QCD simulations of colour-singlet quasi-bound-state formation near the t̅t threshold. The agreement between the data and the models is quantified via a profile-likelihood fit to the reconstructed 𝑚ₜ-ₜ distributions, in bins of two angular observables sensitive to spin-correlations in the t̅t system. An excess of events is observed over the baseline perturbative QCD prediction, with an observed significance over 8 standard deviations. This excess is consistent with the formation of colour-singlet and spin-singlet 𝑆-wave quasi-bound t̅t states, as predicted by non-relativistic QCD, and corresponds to an observed cross-section of 9.3+1.4 −1.3 pb. |
| Document Type: |
article in journal/newspaper |
| File Description: |
text |
| Language: |
English |
| Relation: |
https://eprints.gla.ac.uk/377309/1/377309.pdf; Collaboration, ATLAS ORCID logoorcid:0000-0002-0560-8985 (2026) Observation of a cross-section enhancement near the t̅t production threshold in √s=13 TeV pp collisions with the ATLAS detector. arXiv , (doi:10.48550/arXiv.2601.11780 ) |
| DOI: |
10.48550/arXiv.2601.11780 |
| Availability: |
https://eprints.gla.ac.uk/377309/; https://eprints.gla.ac.uk/377309/1/377309.pdf; https://doi.org/10.48550/arXiv.2601.11780 |
| Rights: |
cc_by_4 |
| Accession Number: |
edsbas.1DC50B20 |
| Database: |
BASE |