Abstract
We outline a strategy of how to search for QCD instantons of invariant mass 20 -- 60 GeV in diffractive events in low luminosity runs at the LHC. We show that by imposing appropriate selection criteria on the final states, one can select the kinematic regime where the instanton signal exceeds the background by a factor of at least 8. In spite of the relatively strong cuts that we impose on the total transverse energy and the number of charged tracks, $\sum_i E_{T,i}>15$ GeV, $N_{\rm ch}>20$ measured within the $0<\eta<2$ interval and excluding events with high $p_{T}$ particles, the expected cross-section is sufficiently large to study the instanton production in the events with Large Rapidity Gaps at low luminosities, thus avoiding problems with pile-up. The paper also includes an updated computation of instanton cross-sections and other parameters relevant for the ongoing studies.
Highlights
Instantons are nonperturbative classical solutions of Euclidean equations of motion in non-Abelian gauge theories [1]
In spitePof the relatively strong cuts that we impose on the total transverse energy and the number of charged tracks, i ET;i > 15 GeV and Nch > 20 measured within the 0 < η < 2 interval and excluding events with high-pT particles, the expected cross section is sufficiently large to study the instanton production in events with large rapidity gaps at low luminosities, avoiding problems with pileup
The possibility of direct experimental observation of QCD instantons at hadron colliders has recently attracted a fair amount of attention [14,15,49]
Summary
Instantons are nonperturbative classical solutions of Euclidean equations of motion in non-Abelian gauge theories [1]. From the point of view of Feynman graphs, the leadingorder instanton amplitude (4) reveals itself as a family of multiparticle vertices (with different numbers of emitted gluons) integrated over the instanton position and size It describes the emission of a large number of gluons, ng ∝ E2=αs, together with a fixed number of quarks and antiquarks, one pair for each light flavor in accordance with Eq (3). To discover the QCD instanton, we have to observe in the final state a multiparticle cluster or a fireball which contains, in general, a large number of isotropically distributed gluon (mini)jets accompanied by Nf pairs of light quark jets generated by a subprocess such as Eq (3) It is quite challenging, to identify the instanton on top of the underlying event.
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