AugerPrime: Status and first results

David Schmidt (for the Pierre Auger Collaboration)

REVIEW 3 major objections 5 minor 3 cited by

AugerPrime: Status and first results

T0 review · 3 major / 5 minor · reviewed 2026-08-05 · deepseek-v4-flash

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Pith's one-line read The paper reports that the AugerPrime upgrade makes primary mass a per-event observable for ultra-high-energy cosmic rays across nearly the full sky of the 3000 km² surface array, by separating each air shower's signal into electromagnetic

desk verdict A competent, clearly written status report for AugerPrime; the 'first results' are just two demonstration events, and the headline claim about full-sky mass sensitivity is a design expectation, not yet a demonstrated performance. read the letter →

arxiv 2508.08056 v1 pith:ZTNCFERT submitted 2025-08-11 astro-ph.IM hep-ex

David Schmidt (for the Pierre Auger Collaboration) This is my paper · ORCID

classification astro-ph.IMhep-ex PACS 95.55.Vj96.50.sd

keywords ultra-high-energycosmicraysAugerPrimeupgrademasscompositionairshowersscintillatorsurfacedetectorradiomuondetectioninstrumentation

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

The paper reports that the upgraded Pierre Auger Observatory, AugerPrime, turns the mass of the primary cosmic-ray particle into a per-event measurement across effectively the full sky it observes. Until now, mass inferences came mainly from the fluorescence detector's measurement of the depth of shower maximum, which has limited exposure because it only runs on clear, moonless nights. The upgrade adds a scintillator detector and a radio antenna to every water-Cherenkov station, extends the tanks' dynamic range, and buries muon counters in a denser sub-array. Because the scintillator and water-Cherenkov responses to the electromagnetic and muonic components of a shower differ, their signals can be disentangled to expose the muon content—the mass-sensitive quantity—and for highly inclined showers the radio footprint supplies the energy needed to make the water-Cherenkov signal mass-sensitive on its own. If this works as claimed, every high-energy event in the 3000 km² array carries a mass estimate, not just the fraction seen by the fluorescence detector.

What carries the argument

The load-bearing object is the two-component deconvolution of extensive air showers: the ratio of SSD to WCD signals separates the electromagnetic and muonic parts of each shower, because the thin scintillator responds mainly to the electromagnetic component while the deep water-Cherenkov tank responds to both, with a muon-dominated tail. Radio energy estimation supplies the missing energy scale for highly inclined showers, and underground shielded scintillators give direct muon counts that anchor the calibration of the muon estimators across the full array.

What would settle it

Take events seen simultaneously by the upgraded surface array and the fluorescence detector: the per-event mass or muon-content estimate from the SSD/WCD/radio combination must agree with the directly measured X_max within quoted systematic uncertainties, and in the instrumented 20 km² sector the muon content derived from SSD+WCD must match the underground muon counts. A residual bias resembling the known ~30 g/cm² DNN X_max bias, or a discontinuity in the inferred mass near the ~60° zenith angle where the method switches from SSD-based to radio-based, would falsify the claim of full-sky mass

Watch

Extended reading notes

Core claim

The central claim is that mass sensitivity is achieved for effectively the full sky observed with Auger. For zenith angles θ ≲ 60°, the scintillator surface detector (SSD) and the water-Cherenkov detector (WCD) respond differently to the electromagnetic and muonic components of an air shower, so their combined signals can be deconvolved to recover the strength of each component and thereby the primary mass. For more inclined showers (θ ≳ 60°), where the electromagnetic component is heavily attenuated and the SSD's projected area shrinks, the radio detector (RD) measures a sufficiently large footprint to estimate the shower energy; with the energy in hand, the WCD signal—dominated by muons at

Load-bearing premise

The separation of shower signals into electromagnetic and muonic parts by combining SSD, WCD, and radio measurements must stay accurate over the full energy and inclination range without being corrupted by the same simulation-versus-data mismatch that causes the known ~30 g/cm² bias in DNN X_max predictions, and the muon calibration from the small 20 km² underground sector must carry over to the full array.

Editorial extensions

If this is right

Mass-resolved studies of the established UHECR arrival-direction anisotropies become possible, potentially revealing whether the dipole signal is dominated by light or heavy nuclei.
Per-event mass estimates extend to the highest energies, including beyond the observed flux suppression, where the composition is currently least constrained.
Shower-by-shower measurements of the electromagnetic and muonic components up to the highest energies provide direct constraints on hadronic interaction models.
The mass scale established in Phase II can be used to re-analyze and calibrate the large-exposure Phase I water-Cherenkov data set, improving the accuracy of machine-learning reconstructions already applied to it.
The scintillators enable first measurements of the lateral distribution and energy spectrum of neutrons inside air showers, a new window into hadronic interactions.

Reading between the lines

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

The acknowledged ~30 g/cm² bias in DNN-predicted X_max relative to fluorescence measurements is a warning that the new mass estimators, trained on the same air-shower simulations, will likely face a similar simulation-to-data gap; a clean test is to compare full-array mass or muon-content estimates against directly measured X_max on the same events.
The two mass-sensitivity channels meet near θ ≈ 60°; a discontinuity in the inferred mass or muon content across that transition would reveal that the SSD-based and radio-based calibration chains are inconsistent, an issue the paper does not yet address.
The UMD covers only a 20 km² sector; transferring its muon calibration to the full array presumes the sector fairly samples shower muon content across energy and arrival direction, which could fail if composition or interaction properties vary with sky position.
If the full-sky mass tagging holds, the effective exposure for composition studies becomes roughly an order of magnitude larger than the fluorescence detector's, so mass-split anisotropy and spectrum measurements at the highest energies should produce statistically decisive results within the planned ten-year Phase II run.

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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

Short take: this is a solid, mostly descriptive proceedings paper from ICRC. The genuinely new content is the deployment timeline and the two example events; the loaded phrasing in Section 2 — 'mass sensitivity is achieved for effectively the full sky' — outruns the evidence. The paper shows no mass resolution, no bias measurement, and no composition result. That said, it never claims to have measured any physics; it says the upgrade 'will deliver' these capabilities. So the main issue is wording, not substance.

What's good: the hardware milestones are unusually complete and internally consistent — SSD complete 2021, UUB June 2023, RD end 2024, UMD 48/61. The paper is honest about the known ~30 g/cm² bias in DNN-based Xmax predictions and the need to calibrate against direct muon measurements. The two displayed events (multi-hybrid and radio) are appropriate as proof of operation. The heavy self-citation is fine for an instrument paper; it's not circular, and no numerical predictions are made that could be circular.

Where the soft spots are: the 'fully operational' statement in the outlook conflicts with the UMD being 48/61 deployed and commissioning ongoing. And the full-sky mass-sensitivity claim is a design expectation, not a demonstrated result. The stress-test note is right that the UMD calibration is future work, not a current anchor. But the paper itself frames the UMD as calibration for future algorithms, so the flaw is in the strength of the wording, not in the logic.

For a proceedings status paper, this is useful and should be read by anyone tracking AugerPrime's transition to Phase II. A referee should ask for a tense change and a clearer separation between design goals and demonstrated performance, not for new analyses. I'd accept it for peer review with a low bar; it's an instrument status update, not a paper with physics results that need defending.

Referee Report

3 major / 5 minor

Summary. The paper reports the status of the AugerPrime upgrade of the Pierre Auger Observatory. It describes the design and deployment of the scintillator surface detectors (SSDs), radio detectors (RDs), upgraded electronics (UUB), small PMTs, and the underground muon detector (UMD), together with calibration procedures and deployment timelines (SSD complete end 2021, UUB complete June 2023, RD complete end 2024, UMD 48/61 positions). It presents two sample events as first results and argues that the combination of SSD+WCD for inclined angles below about 60 degrees and radio-energy-anchored WCD measurements above that angle provides mass sensitivity for effectively the full sky observed by Auger, with the UMD intended to calibrate the mass estimators.

Significance. If the full-sky mass-sensitivity claim is borne out, AugerPrime Phase II would provide per-event mass estimates for essentially every high-energy event in the 3000 km^2 array, enabling mass-dependent anisotropy studies and composition measurements with an exposure far beyond the fluorescence detector. The paper's strengths are its clear inventory of hardware status, detailed calibration descriptions, and concrete deployment milestones, all of which are credible and internally consistent. Its main weakness is that the central physics-capability claim is stated as a present-day achievement ('mass sensitivity is achieved') while the evidence presented consists of two illustrative events and no quantitative mass resolution, bias, or closure test. The paper is best read as a design and deployment status report, and the wording should reflect that more carefully.

major comments (3)

[Sec. 2, paragraph 3] The sentence 'In this way, mass sensitivity is achieved for effectively the full sky observed with Auger' is stated as a current fact. The only supporting data are the two sample events in Figs. 3 and 4; no mass resolution, bias, or calibration closure is shown. Combined with the acknowledged ~30 g/cm^2 bias in DNN Xmax predictions in Sec. 1, this overstates what has been demonstrated. The claim should be rephrased as a design expectation ('is designed to provide') or supported by quantitative results from the companion papers, with the calibration status of the SSD/WCD and radio/WCD mass estimators explicitly stated.
[Secs. 4 and 5] The phrase 'With AugerPrime now fully operational' and the abstract's 'the enhanced array comes fully online' are inconsistent with the body of the paper: Sec. 4 reports that only 48 of 61 UMD positions are deployed (completion expected end 2025), and Sec. 3.4 states the UMD 'will serve to calibrate' algorithms, not that calibration has been performed. Since the UMD is the proposed anchor for the mass estimators, the paper should distinguish between the main surface array being operational and the full AugerPrime configuration, including calibration, being still in commissioning.
[Sec. 3.4 and Sec. 2] The calibration chain for the full-sky mass sensitivity is not yet demonstrated. The UMD covers only a 20 km^2 sub-array, and the text says it 'will serve to calibrate' the algorithms for the 3000 km^2 array. It is not shown how a calibration derived on this small sector will propagate to the full array, nor is any closure test between UMD muon counts and SSD/WCD-derived muon content presented. At minimum, the authors should either point to companion papers where this calibration strategy is quantitatively validated or explicitly label this as a planned step rather than an accomplished one.

minor comments (5)

[Sec. 1, last paragraph] Typo: 'neutral networks' should be 'neural networks'.
[Sec. 3.3, first sentence after Eq. (1) area] Typo: 'each of the the large WCD PMTs' has a duplicated definite article.
[Fig. 3] The axis label 'Muon Density[1/m2]' lacks a space before the bracket; also the plot uses a malformed superscript in the distance axis label ('1033×102').
[Fig. 2] The y-axis label 'Fraction of Events Containing measurements' mixes capitalization; suggest 'Fraction of events containing measurements'.
[Sec. 4, first paragraph] The phrase 'Exposure for the surface detector of Phase II is already approaching approximately 10% of Phase I' is vague; specify the units (e.g., km^2 sr yr) and the exact reference period for Phase I so the reader can gauge the significance.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the paper is a status report with hardware/design claims, no numerical derivations, and self-citations are independent detector-characterization references.

full rationale

This is a conference status report, not a derivation or prediction paper. The central claim that AugerPrime provides mass sensitivity over nearly the full sky is a design expectation based on the complementary responses of SSD, WCD, and radio detectors; it is not obtained by fitting a parameter to data and then renaming that fit a prediction. No equations are presented that would make an output equal an input by construction. The acknowledged ~30 g/cm^2 bias in DNN Xmax predictions is explicitly stated as a known limitation and a motivation for calibration, not hidden or repackaged as a success. Self-citations to prior collaboration work (e.g., [7]–[21]) are used for detector design, calibration procedures, and performance characterizations; these are not load-bearing circular arguments because they describe independent hardware characterization and prior external measurements, not conclusions derived from the present paper's own data. The UMD is explicitly described as intended 'to calibrate algorithms used to estimate muon content' in the future, and the paper does not claim that calibration has already been achieved. Thus, while the physics-capability claim may outrun the currently shown evidence, that is a strength-of-wording concern, not circularity.

Assumptions & free parameters 0 free parameters · 3 assumptions · 0 invented entities

No new entities are postulated. The paper relies on standard detector response assumptions and on the transfer of calibration from a small sub-array to the full array.

assumptions (3)

domain assumption The SSD response is primarily sensitive to the electromagnetic component and the WCD to the total signal, allowing a two-component deconvolution to obtain EM and muon magnitudes.
Section 2: 'the SSD provides mass sensitivity in that its response to the electromagnetic and muonic shower components differs from that of the WCD. This allows for a deconvolution...' The validity and precision of this deconvolution are not demonstrated in this paper.
domain assumption The radio detector provides an energy estimate for inclined showers that, combined with WCD mass sensitivity, covers the full sky.
Section 2: 'the radio footprint of air showers is sufficiently large at the ground such that the energy of showers can be effectively estimated from its sampling. With the energy of the shower in hand, the WCDs provide the mass-sensitivity for these inclined showers.'
domain assumption The UMD muon measurements can calibrate muon estimators used on the full 3000 km2 array.
Section 2: 'the direct muon measurements will also serve to calibrate algorithms used to estimate muon content with measurements of the upgraded stations of the 3000km2 array.'

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Cite this review

Pith. "Pith review of AugerPrime: Status and first results." pith.science (2026). https://pith.science/paper/ZTNCFERT

@misc{pith2026250808056,
  author       = {Pith},
  title        = {Pith review of: AugerPrime: Status and first results},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/ZTNCFERT}},
  note         = {Machine review of arXiv:2508.08056}
}

read the original abstract

With the knowledge and statistical precision derived from two decades of measurement, the Pierre Auger Observatory has significantly deepened our understanding of ultra-high-energy cosmic rays while unearthing an increasingly complex astrophysical landscape and exposing tensions with hadronic interaction models. The field now demands the mass of individual cosmic-ray primaries as an observable with an exposure that only the 3000-square-kilometer surface array of the Observatory can provide. Access to the primary mass hinges on the disentanglement of the electromagnetic and muonic components of extensive air showers. To achieve this, scintillator and radio detectors have been installed atop each existing water-Cherenkov detector of the surface array, whose dynamic range has also been enhanced through the installation of small-area PMTs. Additionally, the timing and signal resolution of all detector stations have been improved through upgraded station electronics, and underground muon counters have been installed in a region of the array with denser spacing. As the commissioning of the final components of AugerPrime reaches its conclusion and the enhanced array comes fully online, we present the realization of its design, its performance, and the first results from this now multi-hybrid observatory.

Figures

Figures reproduced from arXiv: 2508.08056 by the authors.

**Figure 1.** Left: A fully deployed AugerPrime (Phase II) surface detector station. Right: A counter of the Underground Muon Detector during deployment. exposure of Phase I of the observatory – where only the water-Cherenkov detectors were deployed for the surface detector array – as well as directly improve the precision and accuracy of the predictions of such algorithms by meaningfully contributing to the alignment of the simu… view at source ↗

**Figure 2.** Fraction of events with energies greater than 1018.5 eV containing measurements with the different components of the AugerPrime upgrade during the transition period. The sensitivity of the antennas lies in the frequency range of 30 to 80 MHz in which its response is virtually uniform with low dispersion. The 12-bit, 250 MHz electronics have an amplification of a total of 36 dB and include a band-pass filter in the 3… view at source ↗

**Figure 3.** Lateral distributions of signals from the Water-Cherenkov Detectors, Scintillator Surface Detectors, and Underground Muon Detector for a sample Phase II event. of signals is also improved with the 12-bit UUB electronics, which improve upon the 10-bit UB. The updated GPS receivers also boast an improved timing resolution of 5 ns. To accommodate the increased power consumption particularly due to the RD, new solar pan… view at source ↗

Figures from the paper (1 more)

**Figure 4.** Figure 4: Topology (left) and lateral distribution (right) of energy fluence for a sample inclined event measured with the Radio Detector of Phase II. and was completed at the end of June 2023. Each station in the surface detector array remained in acquisition until the moment i…

Discussion (0). Continue with ORCID to comment.

Forward citations

Cited by 3 Pith papers

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Cosmogenic photon fluxes from ultra-high-energy cosmic rays are predicted for six source scenarios; mixed scenarios without protons lie >1.5 orders below present limits, while some pure-proton parameter combinations a...
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On Understanding of the Dynamics of Model Capacity in Continual Learning
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The abstract and full text are two different papers: the abstract describes continual learning (CLEMC), while the body covers AugerPrime cosmic-ray detectors, so the claimed results are unverifiable from this submission.

Reference graph

Works this paper leans on

22 extracted references · 22 canonical work pages · cited by 3 Pith papers

[1]

Aabet al.[Pierre Auger], Science357, no.6537, 1266-1270 (2017)

A. Aabet al.[Pierre Auger], Science357, no.6537, 1266-1270 (2017)

work page 2017
[2]

A. A. Halimet al.[Pierre Auger], Astrophys. J.976, no.1, 48 (2024)

work page 2024
[3]

Aabet al.[Pierre Auger], Phys

A. Aabet al.[Pierre Auger], Phys. Rev. D90, no.12, 122005 (2014)

work page 2014
[4]

Aabet al.[Pierre Auger], Phys

A. Aabet al.[Pierre Auger], Phys. Rev. D90, no.12, 122006 (2014)

work page 2014
[5]

Abdul Halimet al.[Pierre Auger], Phys

A. Abdul Halimet al.[Pierre Auger], Phys. Rev. D111, no.2, 022003 (2025)

work page 2025
[6]

Abdul Halimet al.[Pierre Auger], Phys

A. Abdul Halimet al.[Pierre Auger], Phys. Rev. Lett.134, no.2, 021001 (2025)

work page 2025
[7]

Šmída [Pierre Auger], PoSICRC2017, 390 (2018)

R. Šmída [Pierre Auger], PoSICRC2017, 390 (2018)

work page 2018
[8]

Pekala [Pierre Auger], PoSICRC2019, 380 (2020)

J. Pekala [Pierre Auger], PoSICRC2019, 380 (2020)

work page 2020

Show all 22 references

[9]

Conteet al.[Pierre Auger], these proceedings

M. Conteet al.[Pierre Auger], these proceedings
[10]

Andradaet al.[Pierre Auger], these proceedings

B. Andradaet al.[Pierre Auger], these proceedings
[11]

Pontet al.[Pierre Auger], these proceedings

B. Pontet al.[Pierre Auger], these proceedings
[12]

Abdul Halimet al.[Pierre Auger], PoSICRC2023, 343 (2023)

A. Abdul Halimet al.[Pierre Auger], PoSICRC2023, 343 (2023)

2023
[13]

Bohacovaet al.[Pierre Auger], these proceedings

M. Bohacovaet al.[Pierre Auger], these proceedings
[14]

Abdul Halimet al.[Pierre Auger], JINST18, no.10, P10016 (2023)

A. Abdul Halimet al.[Pierre Auger], JINST18, no.10, P10016 (2023)

2023
[15]

Aabet al.[Pierre Auger], JINST16, no.04, P04003 (2021)

A. Aabet al.[Pierre Auger], JINST16, no.04, P04003 (2021)

2021
[16]

Scornavaccheet al.[Pierre Auger], these proceedings

M. Scornavaccheet al.[Pierre Auger], these proceedings
[17]

de Jesuset al.[Pierre Auger], these proceedings

J. de Jesuset al.[Pierre Auger], these proceedings
[18]

Filipet al.[Pierre Auger], these proceedings

P. Filipet al.[Pierre Auger], these proceedings
[19]

Strähnzet al.[Pierre Auger], these proceedings

S. Strähnzet al.[Pierre Auger], these proceedings
[20]

Stadelmaieret al.[Pierre Auger], these proceedings

M. Stadelmaieret al.[Pierre Auger], these proceedings
[21]

Schoorlemmeret al.[Pierre Auger], these proceedings

H. Schoorlemmeret al.[Pierre Auger], these proceedings
[22]

Tor Vergata

T. Schulzet al.[Pierre Auger], these proceedings. 8 AugerPrime: Status and first results David Schmidt The Pierre Auger Collaboration A. Abdul Halim 13, P. Abreu 70, M. Aglietta 53,51, I. Allekotte 1, K. Almeida Cheminant 78,77, A. Almela7,12, R. Aloisio 44,45, J. Alvarez-Muñi...

2019

Pith tools

Reviewed August 5, 2026 · model on record in the stance chip above.

[1] [1]

Aabet al.[Pierre Auger], Science357, no.6537, 1266-1270 (2017)

A. Aabet al.[Pierre Auger], Science357, no.6537, 1266-1270 (2017)

work page 2017

[2] [2]

A. A. Halimet al.[Pierre Auger], Astrophys. J.976, no.1, 48 (2024)

work page 2024

[3] [3]

Aabet al.[Pierre Auger], Phys

A. Aabet al.[Pierre Auger], Phys. Rev. D90, no.12, 122005 (2014)

work page 2014

[4] [4]

Aabet al.[Pierre Auger], Phys

A. Aabet al.[Pierre Auger], Phys. Rev. D90, no.12, 122006 (2014)

work page 2014

[5] [5]

Abdul Halimet al.[Pierre Auger], Phys

A. Abdul Halimet al.[Pierre Auger], Phys. Rev. D111, no.2, 022003 (2025)

work page 2025

[6] [6]

Abdul Halimet al.[Pierre Auger], Phys

A. Abdul Halimet al.[Pierre Auger], Phys. Rev. Lett.134, no.2, 021001 (2025)

work page 2025

[7] [7]

Šmída [Pierre Auger], PoSICRC2017, 390 (2018)

R. Šmída [Pierre Auger], PoSICRC2017, 390 (2018)

work page 2018

[8] [8]

Pekala [Pierre Auger], PoSICRC2019, 380 (2020)

J. Pekala [Pierre Auger], PoSICRC2019, 380 (2020)

work page 2020