Hunting for QCD Instantons

M.G. Ryskin; V.A. Khoze

arxiv: 2606.10588 · v1 · pith:BQDQV26Knew · submitted 2026-06-09 · ✦ hep-ph · hep-ex

Hunting for QCD Instantons

M.G. Ryskin , V.A. Khoze This is my paper

Pith reviewed 2026-06-27 12:31 UTC · model grok-4.3

classification ✦ hep-ph hep-ex

keywords QCD instantonssphaleronsdiffractive eventsrapidity gapshyperon spin correlationsLHCNICAQCD backgrounds

0 comments

The pith

QCD instantons could be detected in diffractive events at the LHC or through hyperon spin correlations at NICA.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper explores experimental signatures for the production of QCD instantons, which are classical solutions describing transitions between different vacuum states and have never been observed. It focuses on distinguishing these events from standard QCD backgrounds by looking for large rapidity gaps in diffractive processes at the LHC and spin-spin correlations between hyperons at the NICA facility. The proposals aim to provide concrete search strategies using existing or near-future collider data.

Core claim

The signatures of instanton and sphaleron production events, such as those with large rapidity gaps and specific spin correlations, can be used to search for QCD instantons in diffractive events at the LHC and via hyperon pairs at NICA, separating them from ordinary QCD backgrounds.

What carries the argument

Instanton (sphaleron) production signatures including diffractive rapidity gaps and hyperon spin-spin correlations that distinguish them from QCD backgrounds.

If this is right

Diffractive events with large rapidity gaps at the LHC offer a channel to isolate instanton signals.
Spin correlations between two hyperons at NICA provide an independent way to search for instantons.
The main QCD backgrounds must be accounted for to claim an instanton signal.
Observation would confirm non-perturbative transitions between QCD vacua.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

If these signatures are observed, it would allow study of baryon number violating processes in QCD.
Similar correlation techniques might apply to other high-energy experiments.
Data from current runs could already test the feasibility of isolating these signals.

Load-bearing premise

The signatures can be experimentally isolated from ordinary QCD backgrounds with sufficient purity.

What would settle it

No excess of events with the predicted rapidity gaps or spin correlations in LHC and NICA data would falsify the proposed search methods.

Figures

Figures reproduced from arXiv: 2606.10588 by M.G. Ryskin, V.A. Khoze.

**Figure 1.** Figure 1: Instanton production in a diffractive process with an LRG. The pomeron exchange is shown by the thick, doubled line. The red bar shows the considered range of η, and Y indicates the incoming proton position in rapidity. As shown in the diagram, some secondaries will be produced outside this range but will not be used when calculating ET or Nch. where i ̸= k and f ̸= i f ̸= k. In comparison with perturbativ… view at source ↗

**Figure 2.** Figure 2: Distribution over the transverse sphericity of the charged hadrons produced in the events with the instanton (green) in comparison with the expected background (red). To confirm that it was the instanton/sphaleron, we could observe a larger than usual (at this energy) multiplicity and a stronger energy (√ s) dependence and/or the additional spin- spin correlation, when the second beam is polarized as wel… view at source ↗

read the original abstract

Instantons are non-perturbative classical solutions which describe transitions between different QCD vacua. They have never been observed experimentally. We consider the signatures of the instanton (sphaleron) production events and the main QCD backgrounds. The possibilities to search for the QCD instantons in the diffractive (i.e. with a large rapidity gap) events at the LHC and via the spin-spin correlations between two hyperons at NICA are discussed.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This is a short proposal for instanton search channels at LHC and NICA that offers no calculations or estimates to show the signatures can beat ordinary QCD backgrounds.

read the letter

The main takeaway is that Ryskin and Khoze suggest looking for QCD instantons in diffractive events with large rapidity gaps at the LHC and through spin-spin correlations of hyperons at NICA. They state that signatures and backgrounds are discussed, but the note contains no cross sections, no rate estimates, and no comparison of distributions that would show whether an instanton signal could actually be isolated.

The paper applies existing ideas about instanton production to these two experimental setups. It does not derive new results or perform new calculations. What it does is flag two observables that are already measured for other purposes and note that they might also be sensitive to instantons. That is a modest service if you are already working in forward physics or hyperon spin studies.

The soft spot is the absence of any quantitative support. The central claim is that these channels constitute viable search strategies, yet nothing in the text demonstrates that the instanton-induced final states differ enough from standard multi-parton QCD processes in rate or shape. The stress-test note is accurate on this point: without even rough numbers the experimental isolation remains an untested assumption. No machine-checked results or external data are involved either.

This note is aimed at a narrow group of phenomenologists and experimentalists already focused on rapidity gaps or hyperon pairs at hadron facilities. A reader in that niche might pick up a quick pointer, but anyone expecting a worked-out analysis or a new theoretical handle will find little to use. The work is coherent on its own terms and does not contain internal contradictions, but it is too preliminary to justify referee time.

I would not bring it to a reading group. I would not cite it. It does not merit sending out for peer review.

Referee Report

1 major / 0 minor

Summary. The manuscript proposes experimental searches for unobserved QCD instantons by considering their production signatures and the main QCD backgrounds. It discusses the possibility of searching in diffractive events featuring large rapidity gaps at the LHC and via spin-spin correlations between hyperons at NICA.

Significance. If the proposed channels can be shown to provide measurable discrimination from standard QCD processes, the work would be significant because it addresses the experimental absence of instantons and identifies potential probes using existing collider facilities.

major comments (1)

[Abstract] Abstract: The central claim that diffractive rapidity gaps at the LHC and hyperon spin correlations at NICA constitute viable search channels rests on the assertion that instanton-induced final states can be isolated from ordinary QCD backgrounds. However, the manuscript provides no cross-section estimates, parton-level comparisons, acceptance/efficiency calculations, or signal-to-background ratios to support this isolation.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful review and for identifying the need for stronger quantitative support in our proposal. We address the major comment below and will revise the manuscript to incorporate additional estimates.

read point-by-point responses

Referee: [Abstract] Abstract: The central claim that diffractive rapidity gaps at the LHC and hyperon spin correlations at NICA constitute viable search channels rests on the assertion that instanton-induced final states can be isolated from ordinary QCD backgrounds. However, the manuscript provides no cross-section estimates, parton-level comparisons, acceptance/efficiency calculations, or signal-to-background ratios to support this isolation.

Authors: We agree that the manuscript, in its present form, does not contain explicit cross-section estimates, parton-level comparisons, or numerical signal-to-background ratios. The work is framed as an exploratory discussion of distinctive signatures (high-multiplicity soft particle production and rapidity gaps for diffractive LHC events; spin correlations for hyperons at NICA) that could in principle discriminate instanton-induced processes from perturbative QCD backgrounds. To address the concern, we will add order-of-magnitude estimates for instanton production rates drawn from the existing literature on sphaleron and instanton cross sections, together with a qualitative discussion of how the proposed observables differ from standard QCD expectations at the parton level. Full acceptance and efficiency calculations would require dedicated experimental input and are outside the scope of this theoretical proposal; we will note this limitation explicitly in the revision. revision: yes

Circularity Check

0 steps flagged

No circularity; proposal paper contains no derivations or self-referential predictions

full rationale

The manuscript is a forward-looking experimental proposal discussing possible signatures (diffractive rapidity gaps at LHC, hyperon spin correlations at NICA) and QCD backgrounds. It presents no equations, fitted parameters, first-principles derivations, or quantitative predictions that could reduce to inputs by construction. No self-citations, ansatze, or uniqueness theorems are invoked in a load-bearing way. The content is self-contained as a discussion of search strategies without any closed logical loop.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Review performed on abstract only; no free parameters, axioms, or invented entities can be extracted from the provided text. Full manuscript would be required to audit these elements.

pith-pipeline@v0.9.1-grok · 5585 in / 1138 out tokens · 19505 ms · 2026-06-27T12:31:07.464229+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

29 extracted references · 8 linked inside Pith

[1]

A. A. Belavin, A. M. Polyakov, A. S. Schwartz and Y. S. Tyupkin, Phys. Lett.59B85 (1975)

1975
[2]

’t Hooft, Phys

G. ’t Hooft, Phys. Rev. D14343 (1976), Erratum: [Phys. Rev. D18 2199 (1978)]

1976
[3]

C. G. Callan, Jr., R. F. Dashen and D. J. Gross, Phys. Lett.63B334 (1976)

1976
[4]

Jackiw and C

R. Jackiw and C. Rebbi, Phys. Rev. Lett.37172 (1976)

1976
[5]

’t Hooft, Phys

G. ’t Hooft, Phys. Rept.142357 (1986)

1986
[6]

C. G. Callan, Jr., R. F. Dashen and D. J. Gross, Phys. Rev. D172717 (1978)

1978
[7]

V. A. Novikov, M. A. Shifman, A. I. Vainshtein and V. I. Zakharov, Nucl. Phys. B191301 (1981

1981
[8]

E. V. Shuryak, Nucl. Phys. B203116 (1982

1982
[9]

Diakonov and V

D. Diakonov and V. Y. Petrov, Phys. Lett.147B351 (1984). 8

1984
[10]

Diakonov and V

D. Diakonov and V. Y. Petrov, Nucl. Phys. B272457 (1986)

1986
[11]

Sch¨ afer and E

T. Sch¨ afer and E. V. Shuryak, Rev. Mod. Phys.70323 (1998), arXiv: hep-ph/9610451

Pith/arXiv arXiv 1998
[12]

Bjorken, AIP Conf

J.D. Bjorken, AIP Conf. Proc.549(1), 211–229 (2000). arXiv:hep- ph/0008048

arXiv 2000
[13]

Edward Shuryak, Ismail Zahed, arXiv:2102.00256 [hep-ph]

arXiv
[14]

D67114003 (2003), arXiv: hep-ph/0212125

Valeriu Zetocha, Thomas Sch¨ afer, Phys.Rev. D67114003 (2003), arXiv: hep-ph/0212125

Pith/arXiv arXiv 2003
[15]

I. I. Balitsky and M. G. Ryskin, Phys. Atom. Nucl.56, 1106 (1993) [Yad. Fiz.56N8, 196 (1993)]

1993
[16]

I. I. Balitsky and M. G. Ryskin, Phys. Lett. B296185 (1992)

1992
[17]

V. V. Khoze, F. Krauss and M. Schott, JHEP2004201 (2020), arXiv:1911.09726 [hep-ph]

arXiv 2020
[18]

V. V. Khoze, D. L. Milne and M. Spannowsky, Phys. Rev. D103014017 (2021), arXiv:2010.02287 [hep-ph]

arXiv 2021
[19]

Amoroso, D

S. Amoroso, D. Kar and M. Schott, Eur.Phys.J.C81624 (2021), arXiv:2012.09120 [hep-ph]

arXiv 2021
[20]

Chekhovsky it et al., Phys.Rev.D112112006 (2025), arXiv:2505.17850 [hep-ex]

CMS Collaboration, V. Chekhovsky it et al., Phys.Rev.D112112006 (2025), arXiv:2505.17850 [hep-ex]

arXiv 2025
[21]

Guina, S

S. Guina, S. Taha, N. R. Sahooc. and S. Sharmaa, arXiv:2604.20780 [hep-ph]

Pith/arXiv arXiv
[22]

S. Moch, A. Ringwald and F. Schrempp, Nucl. Phys. B507134 (1997), arXiv: hep-ph/9609445

Pith/arXiv arXiv 1997
[23]

Ringwald and F

A. Ringwald and F. Schrempp, Phys. Lett. B438217 (1998), arXiv: hep-ph/9806528

Pith/arXiv arXiv 1998
[24]

Adloffet al.[H1 Collaboration], Eur

C. Adloffet al.[H1 Collaboration], Eur. Phys. J. C25495 (2002), arXiv: hep-ex/0205078

Pith/arXiv arXiv 2002
[25]

Chekanovet al.[ZEUS Collaboration], Eur

S. Chekanovet al.[ZEUS Collaboration], Eur. Phys. J. C34(2004), arXiv: hep-ex/0312048

Pith/arXiv arXiv 2004
[26]

Sas and J

M. Sas and J. Schoppink, arXiv:2101.12367 [hep-ph]

arXiv
[27]

V. A. Khoze, A. D. Martin and M. G. Ryskin, J. Phys. G45053002 (2018), arXiv:1710.11505 [hep-ph]

Pith/arXiv arXiv 2018
[28]

V. V. Khoze, V. A. Khoze, D. L. Milne and M. G. Ryskin, Phys.Rev.D 104054013 (2021), arXiv: 2104.01861 [hep-ph]

arXiv 2021
[29]

M. G. Ryskin, Eur.Phys.J.C83674 (2023), arXiv:2304.07528 [hep-ph]. 9

arXiv 2023

[1] [1]

A. A. Belavin, A. M. Polyakov, A. S. Schwartz and Y. S. Tyupkin, Phys. Lett.59B85 (1975)

1975

[2] [2]

’t Hooft, Phys

G. ’t Hooft, Phys. Rev. D14343 (1976), Erratum: [Phys. Rev. D18 2199 (1978)]

1976

[3] [3]

C. G. Callan, Jr., R. F. Dashen and D. J. Gross, Phys. Lett.63B334 (1976)

1976

[4] [4]

Jackiw and C

R. Jackiw and C. Rebbi, Phys. Rev. Lett.37172 (1976)

1976

[5] [5]

’t Hooft, Phys

G. ’t Hooft, Phys. Rept.142357 (1986)

1986

[6] [6]

C. G. Callan, Jr., R. F. Dashen and D. J. Gross, Phys. Rev. D172717 (1978)

1978

[7] [7]

V. A. Novikov, M. A. Shifman, A. I. Vainshtein and V. I. Zakharov, Nucl. Phys. B191301 (1981

1981

[8] [8]

E. V. Shuryak, Nucl. Phys. B203116 (1982

1982

[9] [9]

Diakonov and V

D. Diakonov and V. Y. Petrov, Phys. Lett.147B351 (1984). 8

1984

[10] [10]

Diakonov and V

D. Diakonov and V. Y. Petrov, Nucl. Phys. B272457 (1986)

1986

[11] [11]

Sch¨ afer and E

T. Sch¨ afer and E. V. Shuryak, Rev. Mod. Phys.70323 (1998), arXiv: hep-ph/9610451

Pith/arXiv arXiv 1998

[12] [12]

Bjorken, AIP Conf

J.D. Bjorken, AIP Conf. Proc.549(1), 211–229 (2000). arXiv:hep- ph/0008048

arXiv 2000

[13] [13]

Edward Shuryak, Ismail Zahed, arXiv:2102.00256 [hep-ph]

arXiv

[14] [14]

D67114003 (2003), arXiv: hep-ph/0212125

Valeriu Zetocha, Thomas Sch¨ afer, Phys.Rev. D67114003 (2003), arXiv: hep-ph/0212125

Pith/arXiv arXiv 2003

[15] [15]

I. I. Balitsky and M. G. Ryskin, Phys. Atom. Nucl.56, 1106 (1993) [Yad. Fiz.56N8, 196 (1993)]

1993

[16] [16]

I. I. Balitsky and M. G. Ryskin, Phys. Lett. B296185 (1992)

1992

[17] [17]

V. V. Khoze, F. Krauss and M. Schott, JHEP2004201 (2020), arXiv:1911.09726 [hep-ph]

arXiv 2020

[18] [18]

V. V. Khoze, D. L. Milne and M. Spannowsky, Phys. Rev. D103014017 (2021), arXiv:2010.02287 [hep-ph]

arXiv 2021

[19] [19]

Amoroso, D

S. Amoroso, D. Kar and M. Schott, Eur.Phys.J.C81624 (2021), arXiv:2012.09120 [hep-ph]

arXiv 2021

[20] [20]

Chekhovsky it et al., Phys.Rev.D112112006 (2025), arXiv:2505.17850 [hep-ex]

CMS Collaboration, V. Chekhovsky it et al., Phys.Rev.D112112006 (2025), arXiv:2505.17850 [hep-ex]

arXiv 2025

[21] [21]

Guina, S

S. Guina, S. Taha, N. R. Sahooc. and S. Sharmaa, arXiv:2604.20780 [hep-ph]

Pith/arXiv arXiv

[22] [22]

S. Moch, A. Ringwald and F. Schrempp, Nucl. Phys. B507134 (1997), arXiv: hep-ph/9609445

Pith/arXiv arXiv 1997

[23] [23]

Ringwald and F

A. Ringwald and F. Schrempp, Phys. Lett. B438217 (1998), arXiv: hep-ph/9806528

Pith/arXiv arXiv 1998

[24] [24]

Adloffet al.[H1 Collaboration], Eur

C. Adloffet al.[H1 Collaboration], Eur. Phys. J. C25495 (2002), arXiv: hep-ex/0205078

Pith/arXiv arXiv 2002

[25] [25]

Chekanovet al.[ZEUS Collaboration], Eur

S. Chekanovet al.[ZEUS Collaboration], Eur. Phys. J. C34(2004), arXiv: hep-ex/0312048

Pith/arXiv arXiv 2004

[26] [26]

Sas and J

M. Sas and J. Schoppink, arXiv:2101.12367 [hep-ph]

arXiv

[27] [27]

V. A. Khoze, A. D. Martin and M. G. Ryskin, J. Phys. G45053002 (2018), arXiv:1710.11505 [hep-ph]

Pith/arXiv arXiv 2018

[28] [28]

V. V. Khoze, V. A. Khoze, D. L. Milne and M. G. Ryskin, Phys.Rev.D 104054013 (2021), arXiv: 2104.01861 [hep-ph]

arXiv 2021

[29] [29]

M. G. Ryskin, Eur.Phys.J.C83674 (2023), arXiv:2304.07528 [hep-ph]. 9

arXiv 2023