REVIEW 3 major objections 6 minor 71 references
From CREX to CEvNS: The Weak Radius of 40Ar
T0 review · 3 major / 6 minor · reviewed 2026-08-05 · deepseek-v4-flash
Pith's one-line read The paper claims that the weak radius of argon-40—the nuclear observable that controls the loss of coherence in liquid-argon neutrino scattering—is 3.452 ± 0.028 (stat) ± 0.022 (syst) fm, inferred by anchoring to the measured 48Ca weak radi
desk verdict A useful CREX-anchored estimate of the weak radius of 40Ar, with a clean error budget, but the systematic error covers only covariant EDFs and the CREX point is an extrapolation—worth a referee. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is the weak-charge form factor F_wk(Q²), normalized to one at zero momentum transfer, whose small-Q² expansion defines the weak radius through F_wk = 1 − (1/6) Q² R_wk² + ... . The load-bearing mechanism is the linear relation between R_wk^{48} and R_wk^{40}, characterized by an intercept a and slope b; the CREX value for calcium is inserted into that relation, and the uncertainty is propagated with a two-by-two regression covariance matrix plus an intrinsic scatter term.
What would settle it
A calculation using nonrelativistic energy density functionals that yields a calcium–argon correlation slope at the CREX point deviating from the covariant-EDF line by more than the quoted systematic error would falsify the extraction; alternatively, a precise CEvNS measurement on liquid argon that directly determines R_wk^{40} and disagrees with 3.452 fm outside the combined uncertainties would settle the question empirically.
Extended reading notes
Core claim
The central result is a CREX-informed value for the weak radius of 40Ar: R_wk^{40} = 3.452 ± 0.028 (stat) ± 0.022 (syst) fm, obtained from Eq. (13). The author shows that, despite the unresolved CREX–PREX tension, 17 covariant energy density functionals agree that the weak radii of 48Ca and 40Ar are almost perfectly linearly correlated (ρ = 0.99). Rather than trusting any model's absolute prediction for argon, the paper maps the measured CREX value of R_wk^{48} through the correlation, first using the FSUGold2R covariance matrix for the statistical uncertainty and then the 17-functional ensemble for the systematic uncertainty. Inverse-variance weighting of the two estimates gives the final v
Load-bearing premise
The entire extraction rests on the claim that the nearly perfect linear relation between the calcium and argon weak radii holds at the measured calcium point, even though the models used to establish that line all over-predict the calcium measurement and only one family of nuclear models was tested.
Editorial extensions
If this is right
- Liquid-argon CEvNS experiments obtain a ~1% baseline for coherence-loss corrections, sharpening the Standard-Model prediction they compare against.
- Future argon measurements can be checked directly against this benchmark; agreement would validate the method, disagreement would signal missing physics or new physics.
- The approach shows that the CREX–PREX dilemma need not block practical nuclear baselines for CEvNS: a precise anchor plus a robust local correlation can substitute for reliable absolute predictions.
- Searches for neutrino magnetic moments, nonstandard interactions, and other new physics using argon targets inherit a reduced nuclear uncertainty.
Reading between the lines
- The same anchor-plus-correlation strategy could be ported to other detector nuclei: any nucleus with a precisely measured weak radius could anchor a neighbouring isotope of experimental interest, provided the correlation is demonstrated as carefully as it is here for calcium–argon.
- If a future argon CEvNS extraction of R_wk^{40} falls outside the quoted 1% band, the most likely explanation would be that the covariant-EDF correlation misses physics such as pairing in argon or nonrelativistic functional systematics, rather than immediate evidence for new physics.
- The paper implicitly suggests that resolving the CREX–PREX tension is not a prerequisite for useful CEvNS nuclear inputs; a well-chosen local correlation can bypass the global isovector problem that afflicts absolute predictions.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a method to infer the weak radius of 40Ar, R40_wk, by combining the CREX measurement of R48_wk with a strong linear correlation between the weak radii of 48Ca and 40Ar obtained from 17 covariant energy density functionals. The statistical uncertainty is derived from the covariance matrix of FSUGold2R, while the systematic uncertainty is estimated from the spread of the 17 EDFs. The final result, Eq. (13), is R40_wk = 3.452 ± 0.028 (stat) ± 0.022 (syst) fm. The author frames this as a benchmark for liquid-argon CEvNS experiments, arguing that the weak radius controls the loss of coherence at small momentum transfers. The paper is transparent about several caveats, including the single-family nature of the functionals and the open-shell character of 40Ar, but argues that the strong Ca-Ar correlation makes the method robust.
Significance. If the result holds, it provides one of the first experimentally anchored estimates of the weak radius of 40Ar, a quantity directly relevant to interpreting coherent elastic neutrino-nucleus scattering in liquid-argon detectors. The approach of using CREX to anchor a correlated neighboring nucleus is a useful strategy for circumventing the CREX-PREX dilemma in cases where direct measurements are unavailable. The error propagation in Eqs. (9)-(10) is clear and the paper explicitly lists limitations, which is a strength. However, the central claim of a 'robust baseline' rests on the untested assumption that the Ca-Ar correlation—derived entirely from covariant EDFs and extrapolated below all model predictions—remains valid for other model families. This is the principal risk to the significance of the result.
major comments (3)
- [§III C, Fig. 6, Eq. (12)] The systematic uncertainty is based exclusively on 17 covariant EDFs sharing the same functional form. As the author notes in Sec. IV, this does not capture possible model-family differences. More importantly, the CREX central value lies below every model prediction in Fig. 6, so the extraction is an extrapolation, not an interpolation. The central value is linearly related to the slope of the R48-R40 relation, and a change in that slope of only ~1% would shift R40_wk by ~0.035 fm, exceeding the quoted systematic error of 0.022 fm. The paper should either include an independent model family (e.g., nonrelativistic Skyrme or Fayans EDFs) to test the correlation, or augment the systematic uncertainty to reflect the model-family spread and soften the 'robust baseline' language.
- [§III B, Eq. (10)-(11)] The statistical uncertainty is derived from the covariance matrix of FSUGold2R alone. This covariance matrix depends on the specific calibration set and fitting protocol, including the chiral-EFT input that strongly influences the isovector sector. What is labeled 'stat' is therefore conditional on the chosen model and calibration choices; it does not include systematic effects from the choice of functional form or fitting protocol. This is not a fatal flaw, but the interpretation of the 0.028 fm as a pure statistical error should be clarified, and a more conservative label such as 'parameter uncertainty' may be appropriate.
- [§IV, second caveat] The paper acknowledges that 40Ar is not doubly magic and that simple occupancy variations induce changes of order 0.01 fm in R40_wk. This is nearly half the quoted systematic error and suggests that pairing correlations could be a significant missing ingredient. The estimate is based on a simple occupancy variation, not a genuine many-body calculation, so the true effect could be larger. Since the quoted systematic error is meant to cover such model deficiencies, the current value may be underestimated. The author should either provide a more robust treatment of pairing or increase the systematic uncertainty accordingly.
minor comments (6)
- [Abstract and Sec. IV] The abstract and conclusions call the result a 'robust baseline,' but the caveats listed in Sec. IV indicate significant model dependence. Suggest tempering the language, e.g., 'a model-dependent estimate pending broader validation.'
- [§III B] Typo: 'cross ection' should be 'cross section' in the text following Eq. (5).
- [§II B, Eq. (8)] The definition of L2 uses Φ, Wμ, and Bμ with different normalization; a brief explanation of the transformed fields would improve readability, especially for readers not familiar with the Walecka model conventions.
- [§III C, Fig. 6] The error bars on the individual model predictions are not shown in Fig. 6, making it difficult to assess the weight of each point in the linear regression. Including the covariance-matrix error bars or stating that the regression treats the points as exact would clarify the procedure.
- [§III C] The regression in Fig. 6 is performed on 17 discrete model points without accounting for the fact that several of these functionals are variants of the same underlying form. This may underestimate the effective number of independent models; a brief discussion would help.
- [General] The covariance matrices for FSUGold2 and FSUGold2R are stated to be 'available from the author upon request.' For reproducibility, consider providing them as supplementary material or in a public repository.
Circularity Check
No significant circularity: R40wk is anchored to external CREX measurement; model correlation is not fitted to the target.
full rationale
The paper's derivation chain is: (1) adopt the external CREX measurement R48wk = 3.636 ± 0.035 fm; (2) obtain a linear relation between R48wk and R40wk either from the FSUGold2R covariance matrix (Sec. III B, Figs. 4-5) or from an ensemble of 17 covariant EDFs (Sec. III C, Fig. 6); and (3) insert the CREX value into the resulting regression to produce R40wk via Eqs. (9)-(10), yielding Eqs. (11)-(13). The target quantity R40wk is never used as an input: no 40Ar weak-radius measurement is fitted, and the regression slope/intercept are computed purely from model predictions for the two nuclei. The CREX value lies below all model points in Fig. 6, so the procedure is an extrapolation along a model-derived correlation, not an interpolation or a fit to the output. The correlation itself is a computed model prediction, not an imported self-citation or an unverified uniqueness theorem; the cited works [23, 25, 34] provide the functionals and calibrations, but the linear relation is explicitly recalculated here. The paper's own caveats in Sec. IV about using only one family of covariant EDFs, possible pairing effects in 40Ar, and spin-orbit corrections are honest statements of model uncertainty, not evidence that the result is circular. All central ingredients (CREX value, model covariance, EDF predictions) are independent of the claimed final value. There is therefore no step in which a fitted parameter is renamed as a prediction or in which a result is equivalent to its inputs by construction.
Assumptions & free parameters
assumptions (4)
- domain assumption CREX's R^48_wk = 3.636 ± 0.035 fm is accurate and normally distributed.
- standard math The weak-form-factor expansion F_wk(Q^2) ≈ 1 - Q^2 R_wk^2/6 is the correct small-Q^2 description.
- ad hoc to paper R^48_wk and R^40_wk are linearly related with ρ ≈ 0.99 as predicted by covariant EDFs, and this linearity survives at the CREX value and across untested model families.
- standard math Statistical uncertainty propagates through a 2x2 linear-regression covariance matrix, Eq. (10).
Cite this review
Pith. "Pith review of From CREX to CEvNS: The Weak Radius of 40Ar." pith.science (2026). https://pith.science/paper/NF2GRVVZ
@misc{pith2026250903645,
author = {Pith},
title = {Pith review of: From CREX to CEvNS: The Weak Radius of 40Ar},
year = {2026},
howpublished = {\url{https://pith.science/paper/NF2GRVVZ}},
note = {Machine review of arXiv:2509.03645}
}
abstract
Despite significant theoretical efforts, the CREX-PREX dilemma remains unresolved, preventing the reliable prediction of neutron (or weak-charge) radii that, besides their intrinsic nuclear-structure interest, often serve to quantify the impact of nuclear uncertainties in searches for new physics. Coherent elastic neutrino-nucleus scattering is a clean and attractive portal to new physics whose sensitivity may be impacted by such nuclear uncertainties. In this paper we use CREX as our main anchor, together with a strong calcium-argon correlation, to provide a robust baseline for the weak radius of ${}^{40}$Ar: $R_{\rm wk}^{\,40} = 3.452 \pm 0.028~\text{(stat)} \pm 0.022~\text{(syst)}\,\text{fm}$.The weak radius of argon is an observable highly relevant to ongoing and future liquid-argon campaigns that encodes the loss of coherence at small momentum transfers.
Figures
Figures from the paper (3 more)
Reference graph
Works this paper leans on
-
[1]
D. Z. Freedman, Phys. Rev. D9, 1389 (1974)
1974
-
[2]
Akimov et al., Science 357, 1123 (2017)
D. Akimov et al., Science 357, 1123 (2017)
2017
- [3]
-
[4]
K. M. Patton, G. C. McLaughlin, and K. Scholberg, Int. J. Mod. Phys. E22, 1330013 (2013)
work page 2013
-
[5]
M. Cadeddu, C. Giunti, Y . F. Li, and Y . Y . Zhang, Phys. Rev. Lett. 120, 072501 (2018)
work page 2018
-
[6]
J. Yang, J. A. Hernandez, and J. Piekarewicz, Phys. Rev. C100, 054301 (2019)
work page 2019
-
[7]
M. Hoferichter, J. Men ´endez, and A. Schwenk, Phys. Rev. D 102, 074018 (2020)
work page 2020
- [8]
Show all 71 references
-
[9]
Aristizabal Sierra, V
D. Aristizabal Sierra, V . De Romeri, and N. Rojas, Phys. Rev. D 98, 075018 (2018), arXiv:1806.07424 [hep-ph]
2018 arXiv
-
[10]
Aristizabal Sierra, J
D. Aristizabal Sierra, J. Liao, and D. Marfatia, (2019), arXiv:1902.07398 [hep-ph]
2019 arXiv
-
[11]
D. K. Papoulias, T. S. Kosmas, and Y . Kuno, Front. in Phys. 7, 191 (2019)
2019
-
[12]
Abdullah et al., (2022), arXiv:2203.07361 [hep-ph]
M. Abdullah et al., (2022), arXiv:2203.07361 [hep-ph]
2022 arXiv
-
[13]
Hoferichter, P
M. Hoferichter, P. Klos, and A. Schwenk, Phys. Lett. B 746, 410 (2015)
2015
-
[14]
Aalbers et al., J
J. Aalbers et al., J. Phys. G 50, 013001 (2023)
2023
-
[15]
Aprile et al
E. Aprile et al. (XENON), Phys. Rev. Lett.133, 191002 (2024)
2024
-
[16]
C. J. Horowitz, K. J. Coakley, and D. N. McKinsey, Phys. Rev. D68, 023005 (2003)
2003
-
[17]
Scholberg, Ann
K. Scholberg, Ann. Rev. Nucl. Part. Sci. 62, 81 (2012)
2012
-
[18]
Y . J. Ko and H. S. Lee, Astropart. Phys.153, 102890 (2023)
2023
-
[19]
Akimov et al., Phys
D. Akimov et al., Phys. Rev. D 100, 115020 (2019)
2019
- [20]
-
[21]
Akimov et al
D. Akimov et al. (COHERENT), Phys. Rev. Lett. 126, 012002 (2021)
2021
-
[22]
F. J. Fattoyev and J. Piekarewicz, Phys. Rev. Lett. 111, 162501 (2013)
2013
-
[23]
Chen and J
W.-C. Chen and J. Piekarewicz, Phys. Rev.C90, 044305 (2014)
2014
-
[24]
Chen and J
W.-C. Chen and J. Piekarewicz, Phys. Lett. B748, 284 (2015)
2015
-
[25]
Salinas and J
M. Salinas and J. Piekarewicz, Phys. Rev. C 107, 045802 (2023)
2023
-
[26]
B. A. Brown, Phys. Rev. Lett. 85, 5296 (2000)
2000
-
[27]
R. J. Furnstahl, Nucl. Phys. A706, 85 (2002)
2002
-
[28]
Roca-Maza, M
X. Roca-Maza, M. Centelles, X. Vi ˜nas, and M. Warda, Phys. Rev. Lett. 106, 252501 (2011)
2011
-
[29]
Donnelly, J
T. Donnelly, J. Dubach, and I. Sick, Nucl. Phys. A503, 589 (1989)
1989
-
[30]
Abrahamyan, Z
S. Abrahamyan, Z. Ahmed, H. Albataineh, K. Aniol, D. S. Armstrong, et al., Phys. Rev. Lett. 108, 112502 (2012)
2012
-
[31]
C. J. Horowitz, Z. Ahmed, C. M. Jen, A. Rakhman, P. A. Souder, et al., Phys. Rev. C85, 032501 (2012)
2012
-
[32]
Adhikari et al
D. Adhikari et al. (PREX), Phys. Rev. Lett.126, 172502 (2021)
2021
-
[33]
Adhikari et al
D. Adhikari et al. (CREX), Phys. Rev. Lett. 129, 042501 (2022)
2022
-
[34]
B. T. Reed, F. J. Fattoyev, C. J. Horowitz, and J. Piekarewicz, Phys. Rev. Lett. 126, 172503 (2021)
2021
-
[35]
C. J. Horowitz and J. Piekarewicz, Phys. Rev. C64, 062802 (2001)
2001
-
[36]
Carriere, C
J. Carriere, C. J. Horowitz, and J. Piekarewicz, Astrophys. J. 593, 463 (2003)
2003
-
[37]
Angeli and K
I. Angeli and K. Marinova, At. Data Nucl. Data Tables 99, 69 (2013)
2013
-
[38]
Hu et al., Nature Phys
B. Hu et al., Nature Phys. 18, 1196 (2022)
2022
-
[39]
Reinhard, X
P.-G. Reinhard, X. Roca-Maza, and W. Nazarewicz, Phys. Rev. Lett. 129, 232501 (2022)
2022
- [40]
-
[41]
Mondal and F
C. Mondal and F. Gulminelli, Phys. Rev. C107, 015801 (2023)
2023
-
[42]
Papakonstantinou (2022) arXiv:2210.02696 [nucl-th]
P. Papakonstantinou (2022) arXiv:2210.02696 [nucl-th]
2022 arXiv
-
[43]
Y ¨uksel and N
E. Y ¨uksel and N. Paar, Phys. Lett. B 836, 137622 (2023)
2023
-
[44]
Li, B.-J
F. Li, B.-J. Cai, Y . Zhou, W.-Z. Jiang, and L.-W. Chen, Astro- phys. J. 929, 183 (2022)
2022
-
[45]
Thakur, R
V . Thakur, R. Kumar, P. Kumar, V . Kumar, M. Kumar, C. Mon- dal, B. K. Agrawal, and S. K. Dhiman, Phys. Rev. C 106, 045806 (2022)
2022
-
[46]
Miyatsu, M.-K
T. Miyatsu, M.-K. Cheoun, K. Kim, and K. Saito, Phys. Lett. B 843, 138013 (2023)
2023
-
[47]
B. T. Reed, F. J. Fattoyev, C. J. Horowitz, and J. Piekarewicz, Phys. Rev. C 109, 035803 (2024)
2024
-
[48]
Sammarruca, Symmetry 16, 34 (2024)
F. Sammarruca, Symmetry 16, 34 (2024)
2024
-
[49]
Salinas and J
M. Salinas and J. Piekarewicz, Phys. Rev. C 109, 045807 (2024)
2024
-
[50]
T.-G. Yue, Z. Zhang, and L.-W. Chen, (2024), arXiv:2406.03844 [nucl-th]
2024
-
[51]
T. Zhao, Z. Lin, B. Kumar, A. W. Steiner, and M. Prakash, (2024), arXiv:2406.05267 [nucl-th]
2024 arXiv
-
[52]
Roca-Maza and D
X. Roca-Maza and D. H. Jakubassa-Amundsen, (2025), arXiv:2501.14375 [nucl-th]
2025 arXiv
-
[53]
Kunjipurayil, J
A. Kunjipurayil, J. Piekarewicz, and M. Salinas, Phys. Rev. C 112, 014310 (2025)
2025
-
[54]
Scholberg, Phys
K. Scholberg, Phys. Rev. D73, 033005 (2006)
2006
-
[55]
Boguta and A
J. Boguta and A. R. Bodmer, Nucl. Phys. A292, 413 (1977)
1977
-
[56]
B. D. Serot and J. D. Walecka, Adv. Nucl. Phys. 16, 1 (1986)
1986
-
[57]
Mueller and B
H. Mueller and B. D. Serot, Nucl. Phys. A606, 508 (1996)
1996
-
[58]
G. A. Lalazissis, J. Konig, and P. Ring, Phys. Rev. C55, 540 (1997)
1997
-
[59]
B. D. Serot and J. D. Walecka, Int. J. Mod. Phys. E6, 515 (1997)
1997
-
[60]
C. J. Horowitz and J. Piekarewicz, Phys. Rev. Lett. 86, 5647 (2001)
2001
-
[61]
B. G. Todd-Rutel and J. Piekarewicz, Phys. Rev. Lett 95, 122501 (2005)
2005
-
[62]
J. D. Walecka, Annals Phys. 83, 491 (1974)
1974
-
[63]
B. P. Abbott et al. (Virgo, LIGO Scientific), Phys. Rev. Lett. 119, 161101 (2017)
2017
-
[64]
B. P. Abbott et al. (Virgo, LIGO Scientific), Phys. Rev. Lett. 121, 161101 (2018)
2018
-
[65]
T. E. Riley et al., Astrophys. J. Lett. 887, L21 (2019)
2019
-
[66]
M. C. Miller et al., Astrophys. J. Lett. 887, L24 (2019)
2019
-
[67]
M. C. Miller et al., Astrophys. J. Lett. 918, L28 (2021)
2021
-
[68]
T. E. Riley et al., Astrophys. J. Lett. 918, L27 (2021)
2021
-
[69]
Drischler, J
C. Drischler, J. W. Holt, and C. Wellenhofer, Ann. Rev. Nucl. Part. Sci. 71, 403 (2021). 8
2021
-
[70]
Piekarewicz, B
J. Piekarewicz, B. Agrawal, G. Col `o, W. Nazarewicz, N. Paar, et al., Phys. Rev. C85, 041302(R) (2012)
2012
-
[71]
C. J. Horowitz and J. Piekarewicz, Phys. Rev. C86, 045503 (2012). ACKNOWLEDGMENTS The author acknowledges many useful discussions with Pablo Giuliani, Caryn Palatchi, and Rex Tayloe. This ma- terial is based upon work supported by the U.S. Department of Energy Office of Scienc...
2012
Reviewed August 5, 2026 · model on record in the stance chip above.
Discussion (0). Sign in to comment.