Central exclusive production at the LHC: Remarks by the organisers on an EMMI workshop

Carlo Ewerz; Otto Nachtmann; Rainer Schicker

REVIEW 2 major objections 4 minor 24 references

Central exclusive production at the LHC: Remarks by the organisers on an EMMI workshop

T0 review · 2 major / 4 minor · reviewed 2026-08-14 · deepseek-v4-flash

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Pith's one-line read The organisers of a workshop on central exclusive production at the LHC conclude that measuring both outgoing protons and the full central final state is the key to studying pomeron couplings, isolating photon exchange, and hunting for…

desk verdict Honest, well-hedged workshop summary on CEP, no new physics; its odderon/glueball optimism is explicitly conditional on forward-detector capabilities the authors themselves flag. read the letter →

arxiv 1908.11792 v1 pith:QA66OOX4 submitted 2019-08-30 hep-ph

Carlo Ewerz , Otto Nachtmann , Rainer Schicker This is my paper · ORCID

classification hep-ph

keywords centralexclusiveproductionodderonglueballpomeronreggeonphotonexchangeforwardprotontaggingLHCdiffraction

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This report from the organisers of an LHC workshop on central exclusive production (CEP) argues that the reaction p + p -> p + X + p, with both protons surviving and large rapidity gaps, is a promising route to three non-perturbative QCD questions: how the pomeron, odderon, reggeons, and photon couple to protons and to the central system X, where odderon effects can first be seen, and what hadronic systems X can be produced. The organisers' bottom line is that CEP offers excellent possibilities for odderon searches and that the search for and characterisation of glueballs are prime topics. They stress that these studies will pay off only if the complete final state can be measured, including the transverse momenta of both outgoing protons and particle identification of the central system. Without such measurements, photon exchange cannot be isolated from odderon backgrounds, and reggeon contributions at pseudorapidities up to about 4 to 5 would be missed.

What carries the argument

The central object is the exclusive reaction $p + p \to p + X + p$ with large rapidity gaps between the surviving protons and the central system $X$, produced by exchange of the pomeron, the odderon, the reggeons, or the photon. The argument is carried by two theoretical tools: an effective model in which charge-conjugation-even exchanges couple as second-rank symmetric tensors while charge-conjugation-odd exchanges couple as vectors, and a resonance ansatz that correlates the production rates of many states lying on a common exchange trajectory. On the experimental side, the load-bearing observable is the pair of proton transverse momenta: their difference defines the glueball-filter variable, their azimuthal angle enters the pomeron-pomeron-$X$ couplings, and their small values isolate photon exchange. Absorption corrections (eikonal and Sudakov suppression) are the main known obstacle, reducing Born-level cross sections by factors of order ten or more.

What would settle it

A decisive check would be a high-statistics LHC run with forward proton tagging at small $|t|$ and full particle identification, searching for CEP signals. If, with these capabilities, no odderon-sensitive asymmetry or glueball-filter enhancement appears above backgrounds, or if it is demonstrated that the required forward coverage cannot be reached, the workshop's central conclusion would be undercut.

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Extended reading notes

Core claim

The organisers' central claim is that central exclusive production at the LHC is a clean and promising arena for non-perturbative QCD. Their conclusions are that CEP allows a detailed study of pomeron couplings, offers excellent possibilities to look for odderon-exchange effects (with great experimental effort required), and offers many opportunities to study hadronic resonances, with glueball search and characterisation as prime topics. They further conclude that these studies benefit considerably if the complete final state can be measured and particle identification is available, because the transverse momenta of the outgoing protons determine the azimuthal angle $\phi_{pp}$ and the glueball-filter variable, and small $|t|$ coverage is needed to isolate photon exchange from odderon backgrounds.

Load-bearing premise

The programme assumes that LHC experiments can measure the outgoing protons at very small transverse momentum (small $|t|$), cover pseudorapidities up to about 4 to 5, and identify the central final-state particles; if they cannot, photon exchange cannot be isolated and odderon effects cannot be separated from backgrounds.

Editorial extensions

If this is right

Measuring the transverse momenta of both outgoing protons determines the azimuthal angle $\phi_{pp}$, needed to pin down the pomeron-pomeron-$X$ couplings.
The glueball-filter variable, the magnitude of the difference of the two proton transverse momenta, is a proposed handle for identifying glueballs in CEP.
Particle identification of the central system's decay products would characterise glueball candidates by their flavour composition.
Reaching small $|t|$ for forward protons is required to isolate photon-exchange CEP and to separate the competing photon background in odderon searches.
Reggeon contributions, though small at central pseudorapidities, become non-negligible for $|\eta|$ up to about 4 to 5, so wide forward coverage is needed.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

A natural next step would be to use photon-exchange CEP in proton-nucleus collisions as a calibration or luminosity channel, since the photon flux differs strongly between proton and nuclear beams but the central system is produced by the same mechanism.
The glueball-filter variable could be tested on existing diffractive data before dedicated forward detectors are upgraded, providing an early check of the filter's discriminating power.
If full final-state measurement is achieved, the same exclusive topology could yield relatively model-independent pomeron couplings by comparing pp, Ap, and AA data, a comparison the report lists as possible but does not develop.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

This is a short organizers' report from a one-day EMMI workshop on central exclusive production at the LHC. There is no new calculation, no data, no derivation; what you get is a clean, honest summary of where the field stands and a set of cautious recommendations. It should be read as a community note, not a research preprint.

It does several things well. The organizers give a balanced picture: they report the tensor-pomeron/vector-odderon effective model as one approach, they mention the Veneziano-type alternative, and they do not hide the fact that the theory is model-based and only partly checked against QCD. They also include Alan Martin's sobering points on absorption suppression (order-of-magnitude reductions) and his view that the existing odderon evidence from elastic scattering is not yet convincing. That is a genuinely useful counterweight to the more optimistic talk summaries. The final bullets are careful: they say CEP "offers excellent possibilities" for odderon searches, but immediately add that this requires great experimental effort, and that isolating photon exchange needs good small-|t| proton tagging, PID, and coverage up to |η| ≈ 4–5.

The soft spots are mostly inherent to the genre. The forward-looking conclusions are opinions formed from talks, not results established in this document; the accuracy of the attributed talk content cannot be verified from the text alone. The stress-test note worries that the odderon/glueball program depends on instrumentation that may not exist. That concern is partly pre-empted by the authors' own hedging: they do not claim these capabilities are currently available, only that the studies would benefit considerably from them. Still, a reader less familiar with LHC forward physics might walk away thinking the program is further along than it is. The paper could have been more explicit about which of these capabilities are planned versus merely desirable.

The self-citations are not a problem here; they point to prior work that underpins the talks and are appropriate in a summary of this kind.

Who is this for? People working on CEP, diffraction, or forward detector planning at the LHC. It is a useful record of where the field stood in 2019 and what the organizers think the priorities should be. I would not bring it to a reading group as a substantive physics paper, and I would not cite it in my own work, but I would point a student to it for a quick orientation.

On peer review: this does not deserve referee time as a research article. It is a workshop report, and the appropriate venue is a proceedings volume or simply the arXiv, where it already lives. A journal that publishes meeting summaries could accept it after a light editorial check, but a serious editor should desk-reject it for a research track.

Referee Report

2 major / 4 minor

Summary. This manuscript is a short document by the organisers of the EMMI workshop 'Central exclusive production at the LHC', held at Heidelberg in February 2019. It records the main topics presented at the meeting: the tensor-pomeron/vector-odderon effective model, a Veneziano-type resonance approach, holographic predictions for glueballs, the GenEx and DRgen event generators, and Alan Martin's discussion of absorption corrections and the status of the odderon. The authors then give their own conclusions, which are that CEP reactions will allow detailed studies of pomeron couplings, offer excellent possibilities for odderon searches, are prime places to search for glueballs, and would benefit considerably from measuring the complete final state with particle identification and forward coverage up to |η| ≈ 4–5.

Significance. The paper contains no new calculations, data, or derivations; its value is as a concise and accessible synthesis of the current state of CEP physics and of the open experimental and theoretical questions. It is useful as a documented starting point for future studies and for experimental planning, and it does a service by explicitly recording caveats, such as Alan Martin's view that existing odderon evidence at small |t| is not yet convincing and that absorption reduces Born-level cross sections by an order of magnitude or more. The strength of the paper is that it honestly reports the model-dependent nature of the theoretical approaches. Its main limitation is that its forward-looking conclusions are optimistic statements conditioned on experimental capabilities that are not demonstrated or referenced in the manuscript.

major comments (2)

[Concluding bullets, p.3] The central claims 'CEP offers excellent possibilities to look for odderon-exchange effects' and that 'the search for and the characterisation of glueballs are prime topics' are presented as unqualified conclusions, yet the same page states that isolating photon exchange and distinguishing odderon contributions requires measurements at very small |t|, and that the relevant reggeon/glueball studies need |η| coverage up to 4–5. The manuscript gives no evidence that current or planned LHC forward detectors (e.g., AFP, CT-PPS, ALFA, or Roman-pot systems) achieve the required small-|t| tag, nor that central PID and pseudorapidity coverage out to 4–5 are available. Since the entire programmatic recommendation depends on this capability, the authors should either cite the actual detector reach or explicitly reframe the conclusions as conditional on future instrumentation. Without this, the proposal is unverified.
[Alan Martin paragraph, p.2, and concluding bullets, p.3] The body reports that eikonal and Sudakov suppression can reduce cross sections by factors of order 10 and larger, and that this absorption must be taken into account in odderon searches. The concluding bullets, however, do not factor this suppression into the claim of 'excellent possibilities', so the summary message is more optimistic than the quantitative evidence presented in the body. The authors should specify whether the proposed CEP studies remain sensitive (e.g., in rate or in observable asymmetries) after the reported suppression, or temper the conclusion accordingly.

minor comments (4)

[Figure 1 caption] The exchange-object labels in the figure caption (intended to show pomeron, odderon, reggeon, and photon lines) appear garbled in the compiled text; the caption should be fixed so that each exchange type is legible.
[Reference [4]] The author name 'A. Schning' should read 'A. Schönning'.
[References [16] and [18]] These references are bare GitHub URLs without commit identifiers or retrieval dates; for archival purposes, the authors should either cite published papers describing the generators or add a retrieval date and version.
[Concluding bullet on reggeons, p.3] The statement that reggeon contributions are 'non-negligible for large |η|' would be clearer with an indication of the kinematic region in mX where this expectation holds, since the size of reggeon contributions is known to depend on the central mass.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the paper is a workshop report with programmatic conclusions, not a derivation whose outputs reduce to its inputs.

full rationale

The document is a set of remarks by the workshop organisers summarising talks and discussions on central exclusive production at the LHC. It contains no derived prediction, no fitted parameter renamed as a result, and no chain of equations whose output is equivalent to an input. The conclusions about odderon searches, glueball studies, and experimental requirements are stated as opinions and outlooks, not as results derived from the cited prior work. The frequent citations to the authors' own papers serve as references to background models and calculations, but none of those references is invoked as the sole load-bearing justification for a new quantitative claim in this report. The report even flags the conditional nature of its outlook by noting that isolating photon exchange and separating odderon effects requires measurements at very small |t| and that reggeon studies require acceptance up to |η| ≈ 4–5. A feasibility assumption is not circular reasoning. Therefore the circularity score is 0.

Assumptions & free parameters 0 free parameters · 2 assumptions · 0 invented entities

No central derivation is attempted, so no free parameters or invented entities appear. The conclusions rest on the feasibility of proposed LHC measurements and on the effective-model framework presented in the cited talks.

assumptions (2)

domain assumption CEP cross sections after absorption are large enough to be measurable despite eikonal and Sudakov suppression factors of order 10 or more.
The report relies on the experimental feasibility of CEP measurements; Alan Martin's talk is cited as emphasizing large reduction factors (References [19,20,21,22,23] section).
domain assumption Forward proton detection with very small transverse momentum resolution and particle identification will be available.
The organizers' recommendations explicitly require these capabilities (last sections under 'We give some examples').

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Cite this review

Pith. "Pith review of Central exclusive production at the LHC: Remarks by the organisers on an EMMI workshop." pith.science (2026). https://pith.science/paper/QA66OOX4

@misc{pith2026190811792,
  author       = {Pith},
  title        = {Pith review of: Central exclusive production at the LHC: Remarks by the organisers on an EMMI workshop},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/QA66OOX4}},
  note         = {Machine review of arXiv:1908.11792}
}

read the original abstract

On February 6, 2019, an EMMI workshop on 'Central exclusive production at the LHC' was held at Heidelberg. Here we make some remarks on the topics presented in the talks and the discussions of this meeting. We hope that this will be useful for further studies of central exclusive reactions.

Figures

Figures reproduced from arXiv: 1908.11792 by the authors.

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

24 extracted references · 12 canonical work pages

[1]

M. G. Albrow, T. D. Coughlin and J. R. Forshaw, Central Exclusive Particle Pro- duction at High Energy Hadron Colliders , Prog. Part. Nucl. Phys. 65 (2010) 149 [arXiv:1006.1289 [hep-ph]]

arXiv 2010
[2]

Ewerz, M

C. Ewerz, M. Maniatis and O. Nachtmann,A Model for Soft High-Energy Scattering: Tensor Pomeron and Vector Odderon, Annals Phys. 342 (2014) 31 [arXiv:1309.3478 [hep-ph]]

arXiv 2014
[3]

Lebiedowicz, O

P. Lebiedowicz, O. Nachtmann and A. Szczurek, Exclusive central diﬀractive pro- duction of scalar and pseudoscalar mesons; tensorial vs. vectorial pomeron , Annals Phys. 344 (2014) 301 [arXiv:1309.3913 [hep-ph]]

arXiv 2014
[4]

A. Bolz, C. Ewerz, M. Maniatis, O. Nachtmann, M. Sauter and A. Schning, Pho- toproduction of π+π− pairs in a model with tensor-pomeron and vector-odderon exchange, JHEP 1501 (2015) 151 [arXiv:1409.8483 [hep-ph]]

arXiv 2015
[5]

Lebiedowicz, O

P. Lebiedowicz, O. Nachtmann and A. Szczurek, Central exclusive diﬀractive pro- duction of K+K−K+K− via the intermediate φφ state in proton-proton collisions , Phys. Rev. D 99 (2019) 094034 [arXiv:1901.11490 [hep-ph]]

arXiv 2019
[6]

Britzger, C

D. Britzger, C. Ewerz, S. Glazov, O. Nachtmann and S. Schmitt, The Tensor Pomeron and Low-x Deep Inelastic Scattering, arXiv:1901.08524 [hep-ph]

arXiv 1901
[7]

Resonance production in Pomeron-Pomeron collisions at the LHC

R. Fiore, L. Jenkovszky and R. Schicker, Resonance production in PomeronPomeron collisions at the LHC , Eur. Phys. J. C 76 (2016) no.1, 38 [arXiv:1512.04977 [hep- ph]]

work page Pith review arXiv 2016
[8]

Exclusive diffractive resonance production in proton-proton collisions at high energies

R. Fiore, L. Jenkovszky and R. Schicker, Exclusive diﬀractive resonance produc- tion in protonproton collisions at high energies , Eur. Phys. J. C 78 (2018) 468 [arXiv:1711.08353 [hep-ph]]

work page Pith review arXiv 2018

Show all 24 references

[9]

Jenkovszky, R

L. Jenkovszky, R. Schicker and I. Szanyi, Elastic and diﬀractive scatterings in the LHC era, Int. J. Mod. Phys. E 27 (2018) 1830005 [arXiv:1902.05614 [hep-ph]]. 4

2018 arXiv
[10]

Br¨ unner and A

F. Br¨ unner and A. Rebhan, Nonchiral enhancement of scalar glueball de- cay in the Witten-Sakai-Sugimoto model , Phys. Rev. Lett. 115 (2015) 131601 [arXiv:1504.05815 [hep-ph]]

2015 arXiv
[11]

Br¨ unner and A

F. Br¨ unner and A. Rebhan, Constraints on the ηη′ decay rate of a scalar glueball from gauge/gravity duality, Phys. Rev. D 92 (2015) 121902 [arXiv:1510.07605 [hep- ph]]

2015 arXiv
[12]

Br¨ unner, D

F. Br¨ unner, D. Parganlija and A. Rebhan, Glueball Decay Rates in the Witten- Sakai-Sugimoto Model, Phys. Rev. D 91 (2015) 106002, Erratum: [Phys. Rev. D 93 (2016) 109903] [arXiv:1501.07906 [hep-ph]]

2015 arXiv
[13]

Br¨ unner, J

F. Br¨ unner, J. Leutgeb and A. Rebhan, A broad pseudovector glueball from holo- graphic QCD, Phys. Lett. B 788 (2019) 431 [arXiv:1807.10164 [hep-ph]]

2019 arXiv
[14]

Imoto, T

T. Imoto, T. Sakai and S. Sugimoto, Mesons as Open Strings in a Holographic Dual of QCD, Prog. Theor. Phys. 124 (2010) 263 [arXiv:1005.0655 [hep-th]]

2010 arXiv
[15]

M. Trzebinski, GenEx - Exclusive Meson Generator , in Proceedings of the 17th conference on Elastic and Diﬀractive scattering (EDS Blois 2017), Prague, Czech Republic, June 26 - 30, 2017; arXiv:1711.03797 [hep-ph]

2017 arXiv
[16]

https://github.com/rkycia/GenEx https://github.com/rkycia/GenExLight
[17]

M. R. Atayan et al. [EHS/NA22 Collaboration], A Study of double pomeron ex- change in π+p and K+p interactions at 250 GeV/c, Z. Phys. C 50 (1991) 353

1991
[18]

https://github.com/alisw/AliRoot https://alice-doc.github.io/alice-analysis-tutorial/
[19]

V. A. Khoze, A. D. Martin and M. G. Ryskin, Multiple interactions and rapidity gap survival, J. Phys. G 45 (2018) 053002 [arXiv:1710.11505 [hep-ph]]

2018 arXiv
[20]

V. A. Khoze, A. D. Martin and M. G. Ryskin, Elastic proton-proton scattering at 13 TeV, Phys. Rev. D 97 (2018) 034019 [arXiv:1712.00325 [hep-ph]]

2018 arXiv
[21]

V. A. Khoze, A. D. Martin and M. G. Ryskin, Elastic and diﬀractive scattering at the LHC, Phys. Lett. B 784 (2018) 192 [arXiv:1806.05970 [hep-ph]]

2018 arXiv
[22]

L. A. Harland-Lang, V. A. Khoze, A. D. Martin and M. G. Ryskin, Searching for the Odderon in Ultraperipheral Proton–Ion Collisions at the LHC , Phys. Rev. D 99 (2019) 034011 [arXiv:1811.12705 [hep-ph]]

2019 arXiv
[23]

L. A. Harland-Lang, V. A. Khoze and M. G. Ryskin, Exclusive LHC physics with heavy ions: SuperChic 3 , Eur. Phys. J. C 79 (2019) 39 [arXiv:1810.06567 [hep-ph]]

2019 arXiv
[24]

F. E. Close and A. Kirk, A Glueball - q¯q ﬁlter in central hadron production , Phys. Lett. B 397 (1997) 333 [hep-ph/9701222]. 5

1997 arXiv

Pith tools

Reviewed August 14, 2026 · model on record in the stance chip above.

[1] [1]

M. G. Albrow, T. D. Coughlin and J. R. Forshaw, Central Exclusive Particle Pro- duction at High Energy Hadron Colliders , Prog. Part. Nucl. Phys. 65 (2010) 149 [arXiv:1006.1289 [hep-ph]]

arXiv 2010

[2] [2]

Ewerz, M

C. Ewerz, M. Maniatis and O. Nachtmann,A Model for Soft High-Energy Scattering: Tensor Pomeron and Vector Odderon, Annals Phys. 342 (2014) 31 [arXiv:1309.3478 [hep-ph]]

arXiv 2014

[3] [3]

Lebiedowicz, O

P. Lebiedowicz, O. Nachtmann and A. Szczurek, Exclusive central diﬀractive pro- duction of scalar and pseudoscalar mesons; tensorial vs. vectorial pomeron , Annals Phys. 344 (2014) 301 [arXiv:1309.3913 [hep-ph]]

arXiv 2014

[4] [4]

A. Bolz, C. Ewerz, M. Maniatis, O. Nachtmann, M. Sauter and A. Schning, Pho- toproduction of π+π− pairs in a model with tensor-pomeron and vector-odderon exchange, JHEP 1501 (2015) 151 [arXiv:1409.8483 [hep-ph]]

arXiv 2015

[5] [5]

Lebiedowicz, O

P. Lebiedowicz, O. Nachtmann and A. Szczurek, Central exclusive diﬀractive pro- duction of K+K−K+K− via the intermediate φφ state in proton-proton collisions , Phys. Rev. D 99 (2019) 094034 [arXiv:1901.11490 [hep-ph]]

arXiv 2019

[6] [6]

Britzger, C

D. Britzger, C. Ewerz, S. Glazov, O. Nachtmann and S. Schmitt, The Tensor Pomeron and Low-x Deep Inelastic Scattering, arXiv:1901.08524 [hep-ph]

arXiv 1901

[7] [7]

Resonance production in Pomeron-Pomeron collisions at the LHC

R. Fiore, L. Jenkovszky and R. Schicker, Resonance production in PomeronPomeron collisions at the LHC , Eur. Phys. J. C 76 (2016) no.1, 38 [arXiv:1512.04977 [hep- ph]]

work page Pith review arXiv 2016

[8] [8]

Exclusive diffractive resonance production in proton-proton collisions at high energies

R. Fiore, L. Jenkovszky and R. Schicker, Exclusive diﬀractive resonance produc- tion in protonproton collisions at high energies , Eur. Phys. J. C 78 (2018) 468 [arXiv:1711.08353 [hep-ph]]

work page Pith review arXiv 2018