Abstract
QCD instantons are non-perturbative phenomena predicted to arise from the strong force, but which have not been directly observed. However, they may appear as a large number of soft jets in LHC collisions. In this paper the authors provide a state-of-the-art calculation of the event rate for these signals by making use of the optical theorem and higher-order contributions. Despite estimating a large cross-section, they find such searches will be difficult due to trigger thresholds and suggest to look for them in data from low-luminosity runs.
Highlights
Instantons are arguably the best motivated nonperturbative effects in the Standard Model (SM), and yet they have not been observed so far
Instantons are the best motivated, yet unobserved, nonperturbative effects predicted by the Standard Model
Being able to study instantons in scattering processes would provide a new window to the phenomenological exploration of the QCD vacuum, and it would allow the tensioning of nonperturbative theoretical methods developed for gauge theories with data
Summary
Instantons are arguably the best motivated nonperturbative effects in the Standard Model (SM), and yet they have not been observed so far. These effects are beyond the reach of ordinary perturbation theory, and in particular in the electroweak theory they lead to the violation of baryon plus lepton number (B þ L), while in QCD instantons processes violate chirality [5,6],. The final integration over the single negative mode that gives rise to the imaginary part of the amplitude, as required by the optical theorem, will be carried out in the saddle-point approximation This provides a more robust prediction leading on average to an order of magnitude increase in instanton partonic cross sections in our case.
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