Any Light Particle Searches with ALPS II: first science results
Pith reviewed 2026-05-21 17:58 UTC · model grok-4.3
The pith
The ALPS II experiment sets a new upper limit of 1.5e-9 GeV^{-1} on the photon coupling of light pseudoscalar particles, a factor of more than 20 tighter than prior bounds.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
No evidence for the existence of axions or similar lightweight particles was found. For pseudoscalar bosons like the axion, with masses below about 0.1 meV, a limit for the di-photon coupling strength of 1.5e-9 1/GeV was achieved at a 95% confidence level. This is more than a factor of 20 improvement compared to all previous similar experiments. Limits on photon interactions were also provided for scalar, vector and tensor bosons.
What carries the argument
The light-shining-through-a-wall regeneration technique, in which a laser photon converts to a hypothetical particle inside a strong magnetic field, traverses an opaque barrier, and reconverts to a detectable photon on the far side.
If this is right
- The new coupling limit narrows the viable parameter space for axion-like particles that could solve the strong CP problem or constitute dark matter.
- Demonstrated long-term stability and calibration accuracy support the planned optical upgrade that targets another two orders of magnitude in sensitivity.
- The same data set supplies exclusion bounds for scalar, vector, and tensor bosons interacting with photons.
- Absence of signal in the current configuration tightens the requirements any future detection claim must satisfy.
Where Pith is reading between the lines
- Continued null results after the upgrade would push theorists toward models with even weaker couplings or entirely different production mechanisms.
- The calibration procedures developed for ALPS II could be adapted to other precision laser experiments seeking rare conversions.
- The improved laboratory bound complements astrophysical and cosmological constraints, potentially excluding certain axion windows that remain open when only one type of bound is considered.
Load-bearing premise
The background model, noise characterization, and optical calibration are accurate enough that any potential signal would have been detected above the stated limit.
What would settle it
Detection of a statistically significant excess of regenerated photons above the measured background in a follow-up run with comparable or better sensitivity would falsify the null result and the quoted coupling bound.
Figures
read the original abstract
The light-shining-through-a-wall experiment ALPS II at DESY in Hamburg searched for axions and similar lightweight particles in its first science campaign from February to May 2024. No evidence for the existence of such particles was found. For pseudoscalar bosons like the axion, with masses below about 0.1 meV, we achieved a limit for the di-photon coupling strength of 1.5e-9 1/GeV at a 95% confidence level. This is more than a factor of 20 improvement compared to all previous similar experiments. We also provide limits on photon interactions for scalar, vector and tensor bosons. An achievement of this first science campaign is the demonstration of stable operation and robust calibration of the complex experiment. Currently, the optical system of ALPS II is being upgraded aiming for another two orders of magnitude sensitivity increase.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents first science results from the ALPS II light-shining-through-a-wall experiment at DESY, with data taken February–May 2024. No evidence for axions or similar light bosons is reported. For pseudoscalars with m < 0.1 meV a 95 % CL upper limit g_{aγγ} < 1.5 × 10^{-9} GeV^{-1} is quoted, stated to be more than a factor of 20 stronger than all prior LSW experiments. Limits are also given for scalar, vector and tensor bosons. The text stresses successful demonstration of stable long-term operation and robust calibration of the complex apparatus, with an optical upgrade path outlined for a further two orders of magnitude in sensitivity.
Significance. If the quoted limit and its uncertainty budget are substantiated, the result marks a clear technical advance for laboratory axion searches. The factor-of-20 improvement over previous LSW runs (ALPS I, OSQAR, etc.) would place the experiment in a new regime of sensitivity, while the documented stable operation provides the necessary foundation for the planned upgrades. The null outcome itself is unsurprising but the calibration and stability achievements are valuable for the field.
major comments (3)
- [Results section] Results section (limit-setting paragraph): the conversion from observed regenerated-photon upper limit to g_{aγγ} is stated but the numerical inputs (P_laser, B-field integral, L, η_regen, T) and their measured values are not tabulated, nor is the explicit formula used for the conversion shown. This information is required to verify the factor-of-20 improvement claim.
- [Calibration and systematics discussion] Calibration and systematics discussion: although 'robust calibration' is asserted, no quantitative propagation of the dominant systematic uncertainties (power-meter traceability, cavity finesse drift, residual-gas birefringence, detector efficiency) into the final 1.5 × 10^{-9} GeV^{-1} bound is provided. If these systematics exceed the statistical component, the improvement factor relative to prior experiments is not yet demonstrated.
- [Data-analysis subsection] Data-analysis subsection: the background model, noise characterization, and the precise statistical procedure (likelihood or frequentist construction) used to extract the 95 % CL photon-rate limit are not described with sufficient detail or supporting figures to allow independent assessment of the no-signal conclusion.
minor comments (2)
- [Figures] Figure captions should explicitly state the live time and magnet configuration used for each data set.
- [Introduction] The exact reference for the ALPS-I limit used in the factor-of-20 comparison should be cited in the text.
Simulated Author's Rebuttal
We thank the referee for the careful and constructive review of our manuscript on the first science results from ALPS II. We address each major comment point by point below. Revisions have been made to the manuscript to provide the requested details, formulas, tables, and expanded descriptions, thereby improving verifiability without altering the reported results or conclusions.
read point-by-point responses
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Referee: [Results section] Results section (limit-setting paragraph): the conversion from observed regenerated-photon upper limit to g_{aγγ} is stated but the numerical inputs (P_laser, B-field integral, L, η_regen, T) and their measured values are not tabulated, nor is the explicit formula used for the conversion shown. This information is required to verify the factor-of-20 improvement claim.
Authors: We agree that tabulating the measured inputs and stating the explicit conversion formula would strengthen the presentation and allow independent verification of the quoted limit and improvement factor. In the revised manuscript, we have added a table in the Results section listing the measured values of P_laser, the magnetic field integral, regeneration length L, regeneration efficiency η_regen, and transmission T. We also explicitly provide the conversion formula relating the upper limit on the regenerated photon rate to g_{aγγ}. These additions substantiate the factor-of-20 improvement relative to prior LSW experiments such as ALPS I and OSQAR. revision: yes
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Referee: [Calibration and systematics discussion] Calibration and systematics discussion: although 'robust calibration' is asserted, no quantitative propagation of the dominant systematic uncertainties (power-meter traceability, cavity finesse drift, residual-gas birefringence, detector efficiency) into the final 1.5 × 10^{-9} GeV^{-1} bound is provided. If these systematics exceed the statistical component, the improvement factor relative to prior experiments is not yet demonstrated.
Authors: We acknowledge the importance of a quantitative uncertainty budget to confirm that systematics do not undermine the claimed sensitivity improvement. Although the original manuscript described the calibration procedures, we have now expanded the Calibration and systematics discussion to include a dedicated table propagating the dominant uncertainties (power-meter traceability, cavity finesse drift, residual-gas birefringence, and detector efficiency) into the final bound. The updated analysis demonstrates that these systematics remain sub-dominant to the statistical component, thereby validating the 1.5 × 10^{-9} GeV^{-1} limit and the overall improvement factor. revision: yes
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Referee: [Data-analysis subsection] Data-analysis subsection: the background model, noise characterization, and the precise statistical procedure (likelihood or frequentist construction) used to extract the 95 % CL photon-rate limit are not described with sufficient detail or supporting figures to allow independent assessment of the no-signal conclusion.
Authors: We agree that greater detail on the background model, noise characterization, and statistical method is needed for independent evaluation of the no-signal result. The revised manuscript expands the Data-analysis subsection to describe the background model (based on sideband and control-region measurements), noise characterization (including power spectral density and stability metrics), and the statistical procedure (a frequentist upper limit derived from a profile likelihood ratio test statistic). A new supporting figure has been added showing the likelihood scan and the construction of the 95% CL photon-rate limit. These changes enable full assessment of the analysis and the null result. revision: yes
Circularity Check
No circularity in experimental limit-setting
full rationale
The paper reports direct experimental results from the ALPS II light-shining-through-a-wall search. The central claim—an upper limit on the axion-photon coupling of 1.5e-9 GeV^{-1} at 95% CL with no detected signal—is obtained by applying the standard theoretical regeneration probability formula to measured quantities (laser power, magnetic field strength and length, optical efficiency, and observed background rate) and performing a statistical analysis. No derivation step reduces by construction to a self-referential definition, a fitted parameter renamed as a prediction, or a load-bearing self-citation chain. The factor-of-20 improvement is stated relative to prior independent experiments. The analysis chain is self-contained against external benchmarks and does not exhibit any of the enumerated circularity patterns.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Axion-photon mixing occurs in external magnetic fields according to standard quantum field theory
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
For pseudoscalar bosons like the axion, with masses below about 0.1 meV, we achieved a limit for the di-photon coupling strength of 1.5e-9 1/GeV at a 95% confidence level.
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IndisputableMonolith/Foundation/AbsoluteFloorClosure.leanabsolute_floor_iff_bare_distinguishability unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Pγ↔ϕ = 1/4 (ω/kϕ) (gϕγγ BL)² |FN,Δ(qL)|²
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Forward citations
Cited by 2 Pith papers
-
Any Light Particle Searches with ALPS II: Description of the first science campaign
ALPS II's initial science run found no evidence for new bosons and set photon-boson conversion sensitivities at a few 10^{-13}.
-
Characterization of a Two-Channel Optical and Near-infrared Transition Edge Sensor System for Rare-Event Searches
A two-channel TES system for 1064 nm achieves 86% efficiency, <7% energy resolution, and <6 mHz background, allowing 5-sigma detection of signals at 2.7e-5 Hz (5e-24 W) in 20 days.
Reference graph
Works this paper leans on
-
[1]
Any Light Particle Searches with ALPS II: first science results
and references therein). This axion was named “in- visible” as its coupling strengths to Standard Model con- stituents are predicted to be proportional tof −1 a . While fa being much larger than the electroweak scale comes with huge experimental challenges, it makes the axion an ideal cold dark matter candidate [6–12], adding strong cosmological motivatio...
work page internal anchor Pith review Pith/arXiv arXiv 2023
-
[2]
and references therein. The golden axion band shows an “artist’s” view on the approximate range given by KSVZ- and DFSZ-inspired models [55–58], while the yellow range refers to a more recent model [52]. The green area shows the result of this analysis; the purple line, the ALPS II prospects. Pγ / Popen (without the systematic uncertainties) via Limit(⊥+∥...
work page 2015
-
[3]
Navaset al.(Particle Data Group), Phys
S. Navaset al.(Particle Data Group), Phys. Rev. D110, 030001 (2024)
work page 2024
-
[4]
R. D. Peccei and H. R. Quinn, Phys. Rev. Lett.38, 1440 (1977)
work page 1977
- [5]
- [6]
-
[7]
P. Sikivie, Phys. Rev. Lett.51, 1415 (1983), [Erratum: Phys.Rev.Lett. 52, 695 (1984)]
work page 1983
-
[8]
L. F. Abbott and P. Sikivie, Phys. Lett. B120, 133 (1983)
work page 1983
- [9]
- [10]
-
[11]
P. Arias, D. Cadamuro, M. Goodsell, J. Jaeckel, J. Re- 8 dondo, and A. Ringwald, JCAP06, 013, arXiv:1201.5902 [hep-ph]
work page internal anchor Pith review Pith/arXiv arXiv
-
[12]
The landscape of QCD axion models
L. Di Luzio, M. Giannotti, E. Nardi, and L. Visinelli, Phys. Rept.870, 1 (2020), arXiv:2003.01100 [hep-ph]
work page internal anchor Pith review Pith/arXiv arXiv 2020
-
[13]
F. Chadha-Day, J. Ellis, and D. J. E. Marsh, Sci. Adv. 8, abj3618 (2022), arXiv:2105.01406 [hep-ph]
-
[14]
C. Er¨ oncel, R. Sato, G. Servant, and P. Sørensen, JCAP 10, 053, arXiv:2206.14259 [hep-ph]
- [15]
-
[16]
J. R. Espinosa, C. Grojean, G. Panico, A. Pomarol, O. Pujol` as, and G. Servant, Phys. Rev. Lett.115, 251803 (2015), arXiv:1506.09217 [hep-ph]
work page internal anchor Pith review Pith/arXiv arXiv 2015
-
[17]
O. Seto and Y. Toda, Phys. Rev. D110, 083501 (2024), arXiv:2405.11869 [astro-ph.CO]
- [18]
-
[19]
A. Arvanitaki, S. Dimopoulos, S. Dubovsky, N. Kaloper, and J. March-Russell, Phys. Rev. D81, 123530 (2010), arXiv:0905.4720 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv 2010
-
[20]
The type IIB string axiverse and its low-energy phenomenology
M. Cicoli, M. Goodsell, and A. Ringwald, JHEP10, 146, arXiv:1206.0819 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv
-
[21]
The Low-Energy Frontier of Particle Physics
J. Jaeckel and A. Ringwald, Ann. Rev. Nucl. Part. Sci. 60, 405 (2010), arXiv:1002.0329 [hep-ph]
work page internal anchor Pith review Pith/arXiv arXiv 2010
-
[22]
L. Hui, Ann. Rev. Astron. Astrophys.59, 247 (2021), arXiv:2101.11735 [astro-ph.CO]
- [23]
-
[24]
P. Sikivie, Rev. Mod. Phys.93, 015004 (2021), arXiv:2003.02206 [hep-ph]
-
[25]
Abelnet al.(IAXO), JHEP05, 137, arXiv:2010.12076 [physics.ins-det]
A. Abelnet al.(IAXO), JHEP05, 137, arXiv:2010.12076 [physics.ins-det]
-
[26]
J. Eggeet al.(MADMAX), Phys. Rev. Lett.134, 151004 (2025), arXiv:2408.02368 [hep-ex]
- [27]
-
[28]
J. Redondo and A. Ringwald, Contemp. Phys.52, 211 (2011), arXiv:1011.3741 [hep-ph]
work page internal anchor Pith review Pith/arXiv arXiv 2011
-
[29]
Optimizing Light-Shining-through-a-Wall Experiments for Axion and other WISP Searches
P. Arias, J. Jaeckel, J. Redondo, and A. Ringwald, Phys. Rev. D82, 115018 (2010), arXiv:1009.4875 [hep-ph]
work page internal anchor Pith review Pith/arXiv arXiv 2010
-
[30]
Resonant laser power build-up in ALPS -- a "light-shining-through-walls" experiment
K. Ehretet al.(ALPS), Nucl. Instrum. Meth. A612, 83 (2009), arXiv:0905.4159 [physics.ins-det]
work page internal anchor Pith review Pith/arXiv arXiv 2009
-
[31]
New ALPS Results on Hidden-Sector Lightweights
K. Ehretet al., Phys. Lett. B689, 149 (2010), arXiv:1004.1313 [hep-ex]
work page internal anchor Pith review Pith/arXiv arXiv 2010
-
[32]
R. Ballouet al.(OSQAR), Phys. Rev. D92, 092002 (2015), arXiv:1506.08082 [hep-ex]
work page internal anchor Pith review Pith/arXiv arXiv 2015
- [33]
-
[34]
A. Ringwald, J. Sch¨ utte-Engel, and C. Tamarit, JCAP 03, 054, arXiv:2011.04731 [hep-ph]
-
[35]
A. de Giorgi, J. Jaeckel, S. Monath, and V. Takhistov, (2025), arXiv:2512.16837 [hep-ph]
-
[36]
C. Garc´ ıa-Cely and A. Ringwald, (2025), arXiv:2511.03707 [hep-ph]
- [37]
-
[38]
Kˇ r´ ıˇ zov´ a,Observational aspects of a massive graviton, Bachelor thesis, Charles U
R. Kˇ r´ ıˇ zov´ a,Observational aspects of a massive graviton, Bachelor thesis, Charles U. (2024)
work page 2024
-
[39]
Any Light Particle Search II -- Technical Design Report
R. B¨ ahreet al., JINST8, T09001, arXiv:1302.5647 [physics.ins-det]. [38]HERA - A Proposal for a Large Electron Proton Colliding Beam Facility at DESY(1981)
work page internal anchor Pith review Pith/arXiv arXiv 1981
- [40]
- [41]
-
[42]
Resonantly Enhanced Axion-Photon Regeneration
P. Sikivie, D. B. Tanner, and K. van Bibber, Phys. Rev. Lett.98, 172002 (2007), arXiv:hep-ph/0701198
work page internal anchor Pith review Pith/arXiv arXiv 2007
- [43]
-
[44]
Horlitz, in10th International Cryogenic Engineering Conference(1984) pp
G. Horlitz, in10th International Cryogenic Engineering Conference(1984) pp. 377–381
work page 1984
-
[45]
C. Albrecht, S. Barbanotti, H. Hintz, K. Jensch, R. Klos, W. Maschmann, O. Sawlanski, M. Stolper, and D. Trines, EPJ Tech. Instrum.8, 5 (2021), arXiv:2004.13441 [physics.ins-det]
- [46]
-
[47]
T. Kozlowskiet al., Opt. Express33, 11153 (2025), arXiv:2408.13218 [physics.optics]
-
[48]
A. D. Spectoret al., (2026), arXiv:2601.18684 [hep-ex]
work page internal anchor Pith review Pith/arXiv arXiv 2026
- [49]
-
[50]
J. A. Rubiera Gimeno, F. Januschek, K.-S. Isleif, A. Lind- ner, M. Meyer, G. Othman, C. Schwemmbauer, and R. Shah, PoSEPS-HEP2023, 567 (2024)
work page 2024
-
[51]
R. D. Cousins and V. L. Highland, Nuclear Instruments and Methods in Physics Research Section A: Acceler- ators, Spectrometers, Detectors and Associated Equip- ment320, 331 (1992)
work page 1992
-
[52]
O’Hare, cajohare/axionlimits: Axionlimits,https:// cajohare.github.io/AxionLimits/(2020)
C. O’Hare, cajohare/axionlimits: Axionlimits,https:// cajohare.github.io/AxionLimits/(2020)
work page 2020
- [53]
- [54]
-
[55]
Altenm¨ ulleret al.(CAST), Phys
K. Altenm¨ ulleret al.(CAST), Phys. Rev. Lett.133, 221005 (2024), arXiv:2406.16840 [hep-ex]
-
[56]
J. E. Kim, Phys. Rev. Lett.43, 103 (1979)
work page 1979
-
[57]
M. Shifman, A. Vainshtein, and V. Zakharov, Nuclear Physics B166, 493 (1980)
work page 1980
-
[58]
M. Dine, W. Fischler, and M. Srednicki, Physics Letters B104, 199 (1981)
work page 1981
-
[59]
A. R. Zhitnitsky, Sov. J. Nucl. Phys.31, 260 (1980)
work page 1980
-
[60]
D. Blas, J. Carlton, and C. McCabe, Phys. Rev. D111, 115020 (2025)
work page 2025
-
[61]
E. Adelberger, B. Heckel, and A. Nelson, Annual Review of Nuclear and Particle Science53, 77–121 (2003)
work page 2003
-
[62]
A. S. Konopliv, S. W. Asmar, W. M. Folkner, ¨Ozg¨ ur Karatekin, D. C. Nunes, S. E. Smrekar, C. F. Yoder, and M. T. Zuber, Icarus211, 401 (2011)
work page 2011
-
[63]
A. Arvanitaki, S. Dimopoulos, and K. Van Tilburg, Phys- ical Review Letters116, 10.1103/physrevlett.116.031102 (2016)
-
[64]
M. Betz, F. Caspers, M. Gasior, M. Thumm, and S. W. Rieger, Physical Review D88, 10.1103/phys- revd.88.075014 (2013)
-
[65]
Redondo, Journal of Cosmology and Astroparticle Physics2008(07), 008
J. Redondo, Journal of Cosmology and Astroparticle Physics2008(07), 008
-
[66]
J. A. R. Cembranos, A. L. Maroto, and H. Villarrubia- Rojo, JHEP09, 104, arXiv:1706.07818 [hep-ph]
work page internal anchor Pith review Pith/arXiv arXiv
discussion (0)
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