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REVIEW 3 major objections 4 minor 55 references

Axion Searches at the CERN SPS: From Their Dawn to Current Prospects

T0 review · 3 major / 4 minor · reviewed 2026-08-06 · deepseek-v4-flash

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Pith's one-line read This review argues that the CERN SPS has become a versatile platform for axion-like particle searches, from Guido Barbiellini's 1982 beam-dump proposal to today's NA64, NA62, FASER and SHiP experiments.

desk verdict A useful mini-review of SPS axion searches, but its tribute framing leans on an unproven claim that Barbiellini directly influenced CHARM. read the letter →

arxiv 2507.18254 v1 pith:OTZ5CFFP submitted 2025-07-24 hep-ex

Paolo Crivelli , Martina Mongillo This is my paper
classification hep-ex
keywords axionaxion-likeparticlesbeamdumpexperimentsCERNSPSNA64NA62fixed-targetPrimakoffeffect
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 review argues that the CERN SPS is not just a historical site for axion searches but a continuing, versatile platform. It traces a line from Guido Barbiellini's 1982 proposal to use a proton beam dump to the modern experiments NA64, NA62, FASER and SHiP, which together cover the MeV-GeV axion-like particle parameter space with complementary production and decay signatures. The case matters because it frames the SPS program as a coherent multi-pronged approach to a gap between collider searches and traditional beam dump strategies. The paper also serves as a tribute to Barbiellini's foresight in suggesting fixed-target axion searches decades before they became mainstream.

What carries the argument

The load-bearing experimental mechanism is the high-intensity beam dump coupled to an instrumented decay volume. In NA64, 100 GeV electrons strike an active electromagnetic calorimeter target, producing ALPs through Primakoff conversion of bremsstrahlung photons in the nuclear field; the experiment then looks for either missing energy, if the ALP escapes the detector, or a displaced vertex from decay $a \to \gamma\gamma$ inside the hadronic calorimeter. In NA62, the mechanism is rare kaon decays such as $K^+ \to \pi^+ a$ with the ALP decaying to leptons, hadrons, or photons. The two signature classes together cover both long-lived and short-lived ALPs.

What would settle it

A search of the CHARM collaboration's 1986 paper and its internal records: if the publication contains no citation to Barbiellini's 1982 workshop report and no correspondence or minutes show awareness of his proposal, then the direct-influence claim is unsupported even though the experimental results would remain valid.

Watch

Extended reading notes

Core claim

On the paper's own terms, the central claim is that the SPS has evolved from the site of a single proposed axion beam-dump search into a multi-experiment platform for axion-like particles. Barbiellini's 1982 workshop proposal is presented as the seed of this program, implemented in the CHARM experiment's 1986 limits on long-lived neutral particles decaying into photon or lepton pairs. The modern thread runs through NA64's world-leading limits on the ALP-photon coupling below 100 MeV, NA62's searches for gluon- and fermion-coupled ALPs in rare kaon decays, and the complementary future reach of FASER and SHiP. The paper concludes that the combined SPS effort now explores the ALP parameter space in the MeV-GeV region more thoroughly than any single experiment could.

Load-bearing premise

The historical thread depends on the claim that Barbiellini's 1982 workshop proposal directly influenced the CHARM collaboration's 1986 analysis, a link asserted without citing evidence that CHARM knew of his proposal.

Editorial extensions

If this is right

  • NA64's planned dataset of $10^{13}$ electrons on target is roughly a factor of 40 larger than the 2020 ALP analysis and should push sensitivity toward higher ALP masses and lower couplings.
  • In the high-coupling region where ALPs decay inside the ECAL and mimic ordinary electromagnetic showers, simply accumulating more statistics gives only marginal improvement, motivating the proposed detector modifications such as a shorter dump and more segmented calorimeters.
  • NA62 is already operating in beam-dump mode and expects new ALP results from the full 2021-2026 dataset.
  • FASER's first ALP results complement NA64 in the regime of smaller couplings and higher masses, while SHiP, under construction, aims to fill sensitivity gaps at heavier masses and smaller couplings.
  • The combined NA64, NA62, FASER and SHiP program is argued to give coherent coverage of the ALP parameter space in the MeV-GeV region at CERN.

Reading between the lines

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

  • If the claimed Barbiellini-to-CHARM influence were confirmed by archival evidence, the intellectual genealogy of beam-dump ALP searches would gain a decade of history; if not, the experimental limits themselves still stand independently of that lineage.
  • The same missing-energy and displaced-vertex toolkit that NA64 uses for ALPs could be applied to other feebly interacting beyond-Standard-Model particles, a direction the paper's closing quote about seeking small unorthodox effects implicitly encourages.
  • The proposed detector upgrades for the high-coupling QCD axion band could be tested first in simulation and then in a dedicated short-dump run, yielding a concrete near-term check of whether the planned sensitivity gains are realized.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

3 major / 4 minor

Summary. This mini-review traces axion and axion-like-particle (ALP) searches at the CERN SPS, from Guido Barbiellini's 1982 workshop proposal through early beam-dump experiments (E137, E141, E774, CHARM, NuCal, NOMAD) to the current NA62 and NA64 programs and the future FASER and SHiP efforts. It is explicitly framed as a tribute to Barbiellini's scientific legacy. The paper contains no new experimental results or derivations; it summarizes published limits, describes the experimental strategies, and outlines planned upgrades and projections.

Significance. The review is useful as a compact documentary entry point to the SPS-based axion search program, collecting primary references and clearly explaining the two main NA64 search signatures (missing energy and displaced vertices). Its value is primarily historical and pedagogical rather than quantitative, as it does not reanalyze data or derive new limits. The review's emphasis on the continuity from Barbiellini's proposal to current experiments is engaging and gives context to ongoing searches, provided the historical causal links are accurate.

major comments (3)
  1. [Section 2.2] The sentence 'This proposal directly influenced the CHARM collaboration's later analysis' is asserted without citing any evidence that CHARM knowingly built on Barbiellini's 1982 workshop contribution. The cited CHARM paper [14] is referenced only for the resulting limits, not for the influence, and no archival record or secondary historical source is given. Because the paper's throughline and conclusion ('building on Guido's original insight') rest on this causal claim, it is load-bearing. The claim should either be supported by a direct citation or archival evidence, or softened to state that Barbiellini's proposal was an early and conceptually similar suggestion that preceded the CHARM analysis.
  2. [Section 2.2] The text states 'In their 1986 publication [14]', but reference [14] is dated 1985 (Phys. Lett. B 157, 458, 1985). This internal inconsistency in the year of the CHARM publication should be corrected, as it appears in the central historical narrative.
  3. [Section 2.3] The text attributes constraints on eV-scale ALPs to 'NOMAD' and cites reference [21], but that reference is a single-author paper by S.N. Gninenko in Nucl. Phys. B Proc. Suppl. 2000, not a NOMAD collaboration publication. This is a factual attribution error. Either cite the actual NOMAD collaboration paper if one exists, or rephrase to attribute the result to Gninenko's analysis.
minor comments (4)
  1. [Section 2.2] The sentence 'axions (a) could be produced through proton-nucleus interactions [15]' cites Donnelly et al. (1978), which is a general theoretical paper on axions, not a specific treatment of proton-nucleus production. A more targeted reference for proton-beam-dump production would be appropriate, or the text should be adjusted to match the scope of the cited work.
  2. [Section 3] The phrase 'setting world-leading limits on the ALP-photon coupling in the mass range below 100 MeV' for the 2020 NA64 result is a strong claim. The limits were competitive and important, but 'world-leading' should be qualified with the specific mass range and compared against contemporaneous constraints (e.g., E137 and NuCal), or softened to 'leading' within the stated mass range.
  3. [Figure 3] The label 'KSVZ DSVZ' in the legend of Figure 3 is likely a typo for 'KSVZ DFSZ'; the text correctly refers to DFSZ [32] and KSVZ [33] models. The figure should be checked for label accuracy.
  4. [Section 5] The concluding sentence 'Try to be a little bit heretic (but not too much!)' is a nice tribute, but it is not introduced as a direct quote with quotation marks; adding quotation marks or an explicit 'as Guido put it' would improve clarity.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: this is a narrative review that summarises independent external experimental results; no derivation reduces to its own inputs.

full rationale

This paper is a perspective/review article, not a derivation. It makes no theoretical predictions, fits no parameters, and contains no equations whose outputs are equivalent to inputs by construction. The ALP search strategies, limits, and projections it describes (SLAC E137, CHARM, NA64, NA62, FASER, SHiP) are all attributed to external publications with independent results. The one arguable weakness is the unsupported historical assertion in Section 2.2 that Barbiellini's 1982 workshop proposal 'directly influenced the CHARM collaboration's later analysis'; no CHARM paper, acknowledgement, or archival source is cited for that causal link. This is an evidentiary or historical-support concern, not circular reasoning: the review's summary of the experimental results and the current SPS programme does not depend on proving that causal link, and nothing in the paper is derived from or reduced to the influence claim. The article is self-contained against external benchmarks, so the appropriate circularity score is 0.

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

This is a review paper with no new derivation, fitting, or postulated entities. It relies entirely on previously published experimental results and theoretical models.

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0 comments
Cite this review

Pith. "Pith review of Axion Searches at the CERN SPS: From Their Dawn to Current Prospects." pith.science (2026). https://pith.science/paper/OTZ5CFFP

@misc{pith2026250718254,
  author       = {Pith},
  title        = {Pith review of: Axion Searches at the CERN SPS: From Their Dawn to Current Prospects},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/OTZ5CFFP}},
  note         = {Machine review of arXiv:2507.18254}
}
read the original abstract

This mini-review traces the evolution of axion searches at the CERN Super Proton Synchrotron (SPS), beginning with the early proposal by Guido Barbiellini in 1982 and culminating in the recent advances of the NA62 and NA64 experiments. We discuss the experimental strategies employed in early beam dump searches, the current status of axion and axion-like particle (ALPs) searches at the CERN SPS and future directions. This review serves as a tribute to Guido Barbiellini's scientific legacy and his visionary contributions to this field.

Figures

Figures reproduced from arXiv: 2507.18254 by the authors.

Figure 1
Figure 1. a) Production of ALPs at e+e- colliders. At LEP, searches were focused at the Z0 pole, while at BELLE II, ALPs are produced via virtual annihilation photon coupling to the ALPs. The signature is either a monophoton (if the ALP decays outside the detector) or a 3-photon final state (if it decays within the detector). b) Example of ALP production at LHC. c) Production of ALPs in an electron beam dump experiment. High-… view at source ↗
Figure 2
Figure 2. Schematic illustration of two possible ALP signatures in the NA64 setup. The ALP is produced via the reaction chain e −Z → e −Zγ followed by γZ → aZ, initiated by 100 GeV electrons interacting in the active electromagnetic calorimeter (ECAL), where Z denotes the nuclei of the target material. Top: in the case of a long-lived ALP, the particle escapes the detector before decaying, resulting in a missing energy signal… view at source ↗
Figure 3
Figure 3. Current bounds for ALPs coupling predominantly to photons in the (ma; gaγγ)- plane as a function of the (pseudo)scalar mass ma. The yellow band represents the parameter space for the benchmark QCD axion (DFSZ [32] and KSVZ [33] models extended with a broader range of E/N values [34,35]). In parallel, the NA62 experiment has also contributed to the search for axion-like particles, particularly via rare kaon decay cha… view at source ↗

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Works this paper leans on

55 extracted references · 18 canonical work pages

  1. [14]

    The North Experimental Area at the Cern Super Proton Synchrotron 2021

    Banerjee, D.; Bernhard, J.; Brugger, M.; Charitonidis, N.; Doble, N.; Gatignon, L.; Gerbershagen, A. The North Experimental Area at the Cern Super Proton Synchrotron 2021. Dedicated to Giorgio Brianti on the 50th anniversary of his founding the SPS Experimental Areas Group of CERN-Lab II and hence initiating the present Enterprise., https://doi.org/10.171...

    doi:10.17181/cern.gp3k.0s1y 2021

  2. [21]

    Light in the beam dump - ALP production from decay photons in proton beam-dumps

    Döbrich, B.; Jaeckel, J.; Spadaro, T. Light in the beam dump - ALP production from decay photons in proton beam-dumps. JHEP 2019, 05, 213, [arXiv:hep-ph/1904.02091]. [Erratum: JHEP 10, 046 (2020)], https://doi.org/10.1007/JHEP05(2019)213

    arXiv 2020

  3. [1]

    Introduction The search for axions and axion-like particles (ALPs) is a very active field trying to address long- standing puzzles in particle physics [1–3]. Originally proposed as a consequence of the Peccei–Quinn mechanism [4] to solve the strong CP problem [5,6], axions are also viable candidates for light, weakly interacting bosons that could account ...

    work page

  4. [2]

    Axion Searches at the CERN SPS: From Their Dawn to Current Prospects

    Early Beam Dump Searches for Axion-Like Particles The experimental pursuit of axions and ALPs dates back to the early 1980s, when several beam dump experiments laid the groundwork for future searches. These efforts were instrumental in developing the conceptual and methodological tools that underpin modern investigations. 2.1. SLAC E137: An Electron Beam ...

    work page Pith review arXiv 1980

  5. [3]

    Modern Axion Searches at the CERN SPS: NA62 and NA64 NA64 represents a new generation fixed-target experiment optimised for the search for Dark Sectors [22,23]. It utilises ∼100 GeV electron [ 24], positron [ 25,26], hadron [ 27] and muon [ 28,29] beams from the CERN SPS, which are directed onto an active target consisting of an electromagnetic calorimete...

    work page 2020

  6. [4]

    Future Prospects at CERN NA64 has already recorded an order of magnitude more data compared to the published results, and plans to collect up to 1013 electrons on target after LS3. This represents an increase by a factor ∼40 in statistics compared to the dataset used in the 2020 ALP analysis, which will boost the experiment’s sensitivity towards the unexp...

    work page 2020

  7. [5]

    Try to be a little bit heretical (but not too much!)

    Conclusion The search for axions and axion-like particles has evolved into one of the most compelling frontiers in the quest to uncover physics beyond the Standard Model. At CERN, the SPS is continuing to serve as a versatile platform for such searches. More than four decades ago, Guido Barbiellini proposed using the SPS beam dump configuration to investi...

    work page

  8. [6]

    Axion Cosmology

    Sikivie, P . Axion Cosmology. Lect. Notes Phys. 2008, 741, 19–50, [astro-ph/0610440]. https://doi.org/10.100 7/978-3-540-73518-2_2

    arXiv 2008

Show all 55 references
  1. [7]

    The Low-Energy Frontier of Particle Physics

    Jaeckel, J.; Ringwald, A. The Low-Energy Frontier of Particle Physics. Ann. Rev. Nucl. Part. Sci. 2010, 60, 405–437, [arXiv:hep-ph/1002.0329]. https://doi.org/10.1146/annurev.nucl.012809.104433

    2010 arXiv

  2. [8]

    New experimental approaches in the search for axion-like particles

    Irastorza, I.G.; Redondo, J. New experimental approaches in the search for axion-like particles. Progress in Particle and Nuclear Physics 2018, 102, 89–159. https://doi.org/https://doi.org/10.1016/j.ppnp.2018.05.003

    2018 doi

  3. [9]

    CP Conservation in the Presence of Instantons

    Peccei, R.D.; Quinn, H.R. CP Conservation in the Presence of Instantons. Phys. Rev. Lett. 1977, 38, 1440–1443. https://doi.org/10.1103/PhysRevLett.38.1440

    1977 doi

  4. [10]

    Problem of Strong P and T Invariance in the Presence of Instantons

    Wilczek, F. Problem of Strong P and T Invariance in the Presence of Instantons. Phys. Rev. Lett. 1978, 40, 279–282. https://doi.org/10.1103/PhysRevLett.40.279

    1978 doi

  5. [11]

    A New Light Boson? Phys

    Weinberg, S. A New Light Boson? Phys. Rev. Lett. 1978, 40, 223–226. https://doi.org/10.1103/PhysRevLett. 40.223

    1978 doi

  6. [12]

    Axion Dark Matter

    Adams, C.B.; et al. Axion Dark Matter. In Proceedings of the Snowmass 2021, 3 2022, [arXiv:hep- ex/2203.14923]

    2021 arXiv

  7. [13]

    Summary Report of the Physics Beyond Colliders Study at CERN 2025

    Alemany Fernández, R.; et al. Summary Report of the Physics Beyond Colliders Study at CERN 2025. [arXiv:hep-ex/2505.00947]

    2025 arXiv

  8. [15]

    Closing the gap between beam dump and colliders: ALP searches with NA64

    Crivelli, P . Closing the gap between beam dump and colliders: ALP searches with NA64. https://ep-news. web.cern.ch/content/closing-gap-between-beam-dump-and-colliders-alps-searches-na64, 2020

    2020

  9. [16]

    Searching for Light Dark Matter and Dark Sectors with the NA64 experiment at the CERN SPS 2025

    Andreev, Y.M.; et al. Searching for Light Dark Matter and Dark Sectors with the NA64 experiment at the CERN SPS 2025. [arXiv:hep-ex/2505.14291]

    2025 arXiv

  10. [17]

    Search for Neutral Metastable Penetrating Particles Produced in the SLAC Beam Dump

    Bjorken, J.D.; Ecklund, S.; Nelson, W.R.; Abashian, A.; Church, C.; Lu, B.; Mo, L.W.; Nunamaker, T.A.; Rassmann, P . Search for Neutral Metastable Penetrating Particles Produced in the SLAC Beam Dump. Phys. Rev. D 1988, 38, 3375. https://doi.org/10.1103/PhysRevD.38.3375

    1988 doi

  11. [18]

    Search for Massive Neutrinos, Axions and SUSY Particles at CERN SPS Energies

    Barbiellini, G. Search for Massive Neutrinos, Axions and SUSY Particles at CERN SPS Energies. In Proceedings of the Workshop on SPS Fixed Target Physics for the Years 1984–1989, 1982. https://cds.cern. ch/record/147478

    1984

  12. [19]

    Search for Axion Like Particle Production in 400-GeV Proton - Copper Interactions

    Bergsma, F.; et al. Search for Axion Like Particle Production in 400-GeV Proton - Copper Interactions. Phys. Lett. B 1985, 157, 458–462. https://doi.org/10.1016/0370-2693(85)90400-9

    1985 doi

  13. [20]

    Do Axions Exist? Phys

    Donnelly, T.W.; Freedman, S.J.; Lytel, R.S.; Peccei, R.D.; Schwartz, M. Do Axions Exist? Phys. Rev. D 1978, 18, 1607. https://doi.org/10.1103/PhysRevD.18.1607

    1978 doi

  14. [22]

    A Search for Short Lived Axions in an Electron Beam Dump Experiment

    Riordan, E.M.; et al. A Search for Short Lived Axions in an Electron Beam Dump Experiment. Phys. Rev. Lett. 1987, 59, 755. https://doi.org/10.1103/PhysRevLett.59.755

    1987 doi

  15. [23]

    A Search for Shortlived Particles Produced in an Electron Beam Dump

    Bross, A.; Crisler, M.; Pordes, S.H.; Volk, J.; Errede, S.; Wrbanek, J. A Search for Shortlived Particles Produced in an Electron Beam Dump. Phys. Rev. Lett. 1991, 67, 2942–2945. https://doi.org/10.1103/PhysRevLett.67.2 942

    1991 doi

  16. [24]

    Mass and Lifetime Limits on New Longlived Particles in 300-GeV/ cπ− Interactions

    Badier, J.; et al. Mass and Lifetime Limits on New Longlived Particles in 300-GeV/ cπ− Interactions. Z. Phys. C 1986, 31, 21. https://doi.org/10.1007/BF01559588

    1986 doi

  17. [25]

    Limits on neutral light scalar and pseudoscalar particles in a proton beam dump experiment

    Blumlein, J.; et al. Limits on neutral light scalar and pseudoscalar particles in a proton beam dump experiment. Z. Phys. C 1991, 51, 341–350. https://doi.org/10.1007/BF01548556

    1991 doi

  18. [26]

    Search for eV (pseudo)scalar penetrating particles in the SPS neutrino beam

    Gninenko, S.N. Search for eV (pseudo)scalar penetrating particles in the SPS neutrino beam. Nucl. Phys. B Proc. Suppl. 2000, 87, 105–107. https://doi.org/10.1016/S0920-5632(00)00646-0

    2000 doi

  19. [27]

    Search for MeV dark photons in a light-shining-through-walls experiment at CERN

    Gninenko, S.N. Search for MeV dark photons in a light-shining-through-walls experiment at CERN. Phys. Rev. D 2014, 89, 075008, [arXiv:hep-ph/1308.6521]. https://doi.org/10.1103/PhysRevD.89.075008

    2014 arXiv

  20. [28]

    Missing energy signature from invisible decays of dark photons at the CERN SPS

    Gninenko, S.N.; Krasnikov, N.V .; Kirsanov, M.M.; Kirpichnikov, D.V . Missing energy signature from invisible decays of dark photons at the CERN SPS. Phys. Rev. D 2016, 94, 095025, [arXiv:hep-ph/1604.08432]. https://doi.org/10.1103/PhysRevD.94.095025. 7 of 8

    2016 arXiv

  21. [29]

    Search for Light Dark Matter with NA64 at CERN

    Andreev, Y.M.; et al. Search for Light Dark Matter with NA64 at CERN. Phys. Rev. Lett. 2023, 131, 161801, [arXiv:hep-ex/2307.02404]. https://doi.org/10.1103/PhysRevLett.131.161801

    2023 arXiv

  22. [30]

    Probing light dark matter with positron beams at NA64.Phys

    Andreev, Y.M.; et al. Probing light dark matter with positron beams at NA64.Phys. Rev. D 2024, 109, L031103, [arXiv:hep-ex/2308.15612]. https://doi.org/10.1103/PhysRevD.109.L031103

    2024 arXiv

  23. [31]

    Proof of principle for a light dark matter search with low-energy positron beams at NA64 2025

    Andreev, Y.M.; et al. Proof of principle for a light dark matter search with low-energy positron beams at NA64 2025. [arXiv:hep-ex/2502.04053]

    2025 arXiv

  24. [32]

    Dark-Sector Search via Pion-Produced η and η’ Mesons Decaying Invisibly in the NA64h Detector

    Andreev, Y.M.; et al. Dark-Sector Search via Pion-Produced η and η’ Mesons Decaying Invisibly in the NA64h Detector. Phys. Rev. Lett. 2024, 133, 121803, [arXiv:hep-ex/2406.01990]. https://doi.org/10.1103/ PhysRevLett.133.121803

    2024 arXiv

  25. [33]

    First Results in the Search for Dark Sectors at NA64 with the CERN SPS High Energy Muon Beam

    Andreev, Y.M.; et al. First Results in the Search for Dark Sectors at NA64 with the CERN SPS High Energy Muon Beam. Phys. Rev. Lett. 2024, 132, 211803, [arXiv:hep-ex/2401.01708]. https://doi.org/10.1103/ PhysRevLett.132.211803

    2024 arXiv

  26. [34]

    Shedding light on dark sectors with high-energy muons at the NA64 experiment at the CERN SPS

    Andreev, Y.M.; et al. Shedding light on dark sectors with high-energy muons at the NA64 experiment at the CERN SPS. Phys. Rev. D 2024, 110, 112015, [arXiv:hep-ex/2409.10128]. https://doi.org/10.1103/PhysRevD. 110.112015

    2024 arXiv

  27. [35]

    Photoproduction of axionlike particles in the NA64 experiment

    Dusaev, R.R.; Kirpichnikov, D.V .; Kirsanov, M.M. Photoproduction of axionlike particles in the NA64 experiment. Phys. Rev. D 2020, 102, 055018, [arXiv:hep-ph/2004.04469]. https://doi.org/10.1103/PhysRevD. 102.055018

    2020 arXiv

  28. [36]

    Search for Axionlike and Scalar Particles with the NA64 Experiment

    Banerjee, D.; et al. Search for Axionlike and Scalar Particles with the NA64 Experiment. Phys. Rev. Lett. 2020, 125, 081801, [arXiv:hep-ex/2005.02710]. https://doi.org/10.1103/PhysRevLett.125.081801

    2020 arXiv

  29. [37]

    A Simple Solution to the Strong CP Problem with a Harmless Axion

    Dine, M.; Fischler, W.; Srednicki, M. A Simple Solution to the Strong CP Problem with a Harmless Axion. Phys. Lett. B 1981, 104, 199–202. https://doi.org/10.1016/0370-2693(81)90590-6

    1981 doi

  30. [38]

    Weak Interaction Singlet and Strong CP Invariance

    Kim, J.E. Weak Interaction Singlet and Strong CP Invariance. Phys. Rev. Lett. 1979, 43, 103. https: //doi.org/10.1103/PhysRevLett.43.103

    1979 doi

  31. [39]

    Review of Particle Physics

    Tanabashi, M.; et al. Review of Particle Physics. Phys. Rev. D 2018, 98, 030001. https://doi.org/10.1103/ PhysRevD.98.030001

    2018

  32. [40]

    Constraints on very light axions from cavity experiments

    Kim, J.E. Constraints on very light axions from cavity experiments. Phys. Rev. D 1998, 58, 055006, [hep-ph/9802220]. https://doi.org/10.1103/PhysRevD.58.055006

    1998 arXiv

  33. [41]

    Proposal to measure the rare decay K+ → π+νν at the CERN SPS 2005

    Anelli, G.; et al. Proposal to measure the rare decay K+ → π+νν at the CERN SPS 2005

    2005

  34. [42]

    The Beam and detector of the NA62 experiment at CERN

    Cortina Gil, E.; et al. The Beam and detector of the NA62 experiment at CERN. JINST 2017, 12, P05025, [arXiv:physics.ins-det/1703.08501]. https://doi.org/10.1088/1748-0221/12/05/P05025

    2017 arXiv

  35. [43]

    Physics Beyond Colliders at CERN: Beyond the Standard Model Working Group Report

    Beacham, J.; et al. Physics Beyond Colliders at CERN: Beyond the Standard Model Working Group Report. J. Phys. G 2020, 47, 010501, [arXiv:hep-ex/1901.09966]. https://doi.org/10.1088/1361-6471/ab4cd2

    2020 arXiv

  36. [44]

    Search for hadronic decays of feebly-interacting particles at NA62

    Cortina Gil, E.; et al. Search for hadronic decays of feebly-interacting particles at NA62. Eur. Phys. J. C 2025, 85, 571, [arXiv:hep-ex/2502.04241]. https://doi.org/10.1140/epjc/s10052-025-14133-w

    2025 arXiv

  37. [45]

    Search forπ0 decays to invisible particles

    Cortina Gil, E.; et al. Search forπ0 decays to invisible particles. JHEP 2021, 02, 201, [arXiv:hep-ex/2010.07644]. https://doi.org/10.1007/JHEP02(2021)201

    2021 arXiv

  38. [46]

    Search for a feebly interacting particle X in the decay K+ → π+X

    Cortina Gil, E.; et al. Search for a feebly interacting particle X in the decay K+ → π+X. JHEP 2021, 03, 058, [arXiv:hep-ex/2011.11329]. https://doi.org/10.1007/JHEP03(2021)058

    2021 arXiv

  39. [47]

    Measurement of the K+ → π+γγ decay

    Cortina Gil, E.; et al. Measurement of the K+ → π+γγ decay. Phys. Lett. B 2024, 850, 138513, [arXiv:hep- ex/2311.01837]. https://doi.org/10.1016/j.physletb.2024.138513

    2024 arXiv

  40. [48]

    Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into e+e− pairs

    Banerjee, D.; et al. Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into e+e− pairs. Phys. Rev. D 2020, 101, 071101, [arXiv:hep-ex/1912.11389]. https://doi.org/10.1103/PhysRevD.101.07 1101

    2020 arXiv

  41. [49]

    Hunting down the X17 boson at the CERN SPS

    Depero, E.; et al. Hunting down the X17 boson at the CERN SPS. Eur. Phys. J. C 2020, 80, 1159, [arXiv:hep- ex/2009.02756]. https://doi.org/10.1140/epjc/s10052-020-08725-x

    2020 arXiv

  42. [50]

    Probing axion and muon-philic new physics with muon beam dump2025

    Li, H.; Liu, Z.; Song, N. Probing axion and muon-philic new physics with muon beam dump2025. [arXiv:hep- ph/2501.06294]

  43. [51]

    Leptophilic ALPs in Laboratory Experiments 2025

    Eberhart, A.; Fedele, M.; Kahlhoefer, F.; Ravensburg, E.; Ziegler, R. Leptophilic ALPs in Laboratory Experiments 2025. [arXiv:hep-ph/2504.05873]

    2025

  44. [52]

    Projection of finalized NA62 beam-dump analyses to the full 2021-2026 statistics 2025

    Jerhot, J. Projection of finalized NA62 beam-dump analyses to the full 2021-2026 statistics 2025

    2021

  45. [53]

    Shining light on the dark sector: search for axion-like particles and other new physics in photonic final states with FASER

    Mammen Abraham, R.; et al. Shining light on the dark sector: search for axion-like particles and other new physics in photonic final states with FASER. JHEP 2025, 01, 199, [arXiv:hep-ex/2410.10363]. https: //doi.org/10.1007/JHEP01(2025)199. 8 of 8

    2025 arXiv

  46. [54]

    ForwArd Search ExpeRiment at the LHC

    Feng, J.L.; Galon, I.; Kling, F.; Trojanowski, S. ForwArd Search ExpeRiment at the LHC. Phys. Rev. D 2018, 97, 035001, [arXiv:hep-ph/1708.09389]. https://doi.org/10.1103/PhysRevD.97.035001

    2018 arXiv

  47. [55]

    The SHiP experiment at the proposed CERN SPS Beam Dump Facility

    Ahdida, C.; et al. The SHiP experiment at the proposed CERN SPS Beam Dump Facility. Eur. Phys. J. C 2022, 82, 486, [arXiv:physics.ins-det/2112.01487]. https://doi.org/10.1140/epjc/s10052-022-10346-5

    2022 arXiv

Pith tools

Reviewed August 6, 2026 · model on record in the stance chip above.