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Observation of a cross-section enhancement near the tt̄ production threshold in √s=13 TeV pp collisions with the ATLAS detector
   

Observation of a cross-section enhancement near the tt̄ production threshold in √s=13 TeV pp collisions with the ATLAS detector

G. Aad, E. Aakvaag, B. Abbott, S. Abdelhameed, K. Abeling, N. J. Abicht, S. H. Abidi, M. Aboelela, A. Aboulhorma, H. Abramowicz, …
Reports on progress in physics, Vol.89(5), 057801
05/01/2026
: https://doi.org/10.1088/1361-6633/ae60a0
:
https://hdl.handle.net/10192/79906
Physics, Multidisciplinary Science & Technology Physical Sciences Physics
A measurement of tt̄ production is presented in the invariant-mass region near the pair production threshold, mtt̄ similar to 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 tt̄ production: a baseline model including only perturbative quantum chromodynamics (pQCD) predictions for the hard process at approximate next-to-next-to leading order accuracy in the strong coupling, and an extended model that, in addition, incorporates non-relativistic QCD simulations that also include the formation of colour-singlet quasi-bound-states near the tt̄ threshold. The agreement between the data and the models is quantified via a profile-likelihood fit to the reconstructed m(tt̄) distributions, in bins of two angular observables sensitive to spin-correlations in the tt̄ system. An excess of events is observed over the baseline pQCD prediction, with an observed significance over 8 standard deviations. This excess is consistent with the formation of colour-singlet and spinsinglet S-wave quasi-bound tt̄ states, as predicted by non-relativistic QCD, and corresponds to an observed cross-section of 9.3- (+1.4)(1.3) pb.

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url
https://doi.org/10.1088/1361-6633/ae60a0
Published (Version of record)
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