uRWELL detector developments at Jefferson Lab for high luminosity experiments

Florian Hauenstein; Huong Nguyen; Kondo Gnanvo; Nilanga Liyanage; Rafayel Paremuzyan; Sara Liyanaarachchi; Stepan Stepanyan

REVIEW 4 major objections 4 minor 13 references

uRWELL detector developments at Jefferson Lab for high luminosity experiments

T0 review · 4 major / 4 minor · reviewed 2026-08-12 · deepseek-v4-flash

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Pith's one-line read A large-area μRWELL detector, the largest built so far, exceeded 90% tracking efficiency in cosmic-ray tests, supporting its use as the high-rate tracker for a future DDVCS measurement at Jefferson Lab.

desk verdict First data on the largest μRWELL yet, but the >90% efficiency number needs a denominator. read the letter →

arxiv 2411.13734 v2 pith:UPVBYK7B submitted 2024-11-20 physics.ins-det

Kondo Gnanvo , Florian Hauenstein , Sara Liyanaarachchi , Nilanga Liyanage , Huong Nguyen , Rafayel Paremuzyan , Stepan Stepanyan This is my paper · ORCID

classification physics.ins-det

keywords μRWELLdetectorsmicro-patterngashigh-luminositytrackingCLAS12upgradeDDVCSPEP-dotgroundingparticleratecapabilityJeffersonLab

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 paper reports Jefferson Lab's development of μRWELL micro-pattern gas detectors for future electron-scattering experiments at luminosities above $10^{37}$ cm$^{-2}$ s$^{-1}$, roughly 100 times the present CLAS12 rate. At such luminosities a tracking detector must tolerate particle fluxes near 1 MHz/cm$^{2}$, and the authors argue that the μRWELL's single amplification stage with a resistive layer can provide this. Their large prototype, the largest μRWELL built to date, reached tracking efficiency above 90% with two gas mixtures, with argon/isobutane giving the better stability. The four small high-rate prototypes have passed initial quality checks but have not yet been run in a high-rate beam; that test is planned for early 2025. The paper therefore establishes readiness for the next step, not yet the high-rate capability itself.

What carries the argument

The central object is the μRWELL detector, a micro-pattern gas detector in which amplification happens in microwells in a polyimide foil and a sputtered diamond-like carbon layer provides charge evacuation and spark suppression. The PEP-dot grounding pattern makes the rate capability explicit by etching grounding dots through the upper copper and Kapton down to the resistive layer; the small prototypes vary the dot pitch, well pitch, and readout geometry to find the configuration that keeps efficiency at high flux. The large prototype uses 1 mm pitch U and V strips at ±10 degrees to test whether long, high-capacitance strips preserve efficiency and noise performance.

What would settle it

Expose the small prototypes to a beam and record efficiency and leakage current versus flux up to $10^6$ cm$^{-2}$ s$^{-1}$; if efficiency drops below the roughly 90% level or discharges appear at the operating voltages found in cosmic tests, the central claim is refuted.

Watch

Extended reading notes

Core claim

The central claim, stated as work in progress, is that μRWELL technology is a practical tracking option for the high-luminosity electron-scattering program at Jefferson Lab, including the never-measured DDVCS reaction. The evidence is a large-area prototype with an isosceles-trapezoid active area 145 cm at the base and 50 cm high, which the authors report as the largest μRWELL detector built so far. In cosmic-ray tests it reached above 90% efficiency for both U and V readout strips with Ar/CO2 (80/20) at 610 V and with Ar/isobutane (90/10) at 490 V; the isobutane mixture avoided the frequent leakage-current spikes seen with the CO2 mixture. The four 10 cm by 10 cm high-rate prototypes, varying PEP-dot pitch, well pitch, and readout, passed initial quality checks, so the remaining step is the planned early-2025 beam test at roughly 1 MHz per square centimeter.

Load-bearing premise

The whole plan assumes that the high efficiency and stable operation measured with slow cosmic-ray particles will still hold at roughly $10^6$ particles cm$^{-2}$ s$^{-1}$.

Editorial extensions

If this is right

If the large-prototype efficiency pattern holds, a μRWELL-based forward tracker can be operated for CLAS12 at twice the standard luminosity, as the upgrade concept in the paper requires.
Argon/isobutane (90/10) is the operating gas of choice for stability, while argon/CO2 remains usable if the high-voltage headroom is accepted.
PEP-dot grounding leaves small periodic dead areas, so a final tracker design must either mask them or overlap detectors to maintain uniform efficiency.
The four small prototypes give a direct comparison of dot pitch, well pitch, and readout type; the 1 cm dot-pitch prototype tests whether denser grounding buys the needed rate capability.
The decisive claim for DDVCS, operation at about 1 MHz per square centimeter, is not yet made by this paper and depends on the early-2025 high-rate test.

Reading between the lines

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

If the high-rate test reproduces the cosmic-ray efficiency, the same detector class could serve other large-acceptance, high-luminosity trackers, since the low material budget and simple construction make it comparatively inexpensive to scale.
The observed dust-induced dead spots suggest the detector is robust to contamination; a practical consequence the paper does not develop is that ease of repair or replacement of the cathode foil should be part of the final mechanical design.
The comparison of dot pitches is essentially a measurement of charge-evacuation time versus dead area; one should expect the rate ceiling to scale with dot density, and the beam test will reveal whether 1 cm pitch is sufficient or 2 cm pitch is already limiting.

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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

I read the μRWELL proceedings from the JLab group. The honest headline: it's a legitimate first report on the largest μRWELL built so far (145x50 cm), with the first cosmic efficiency curves for that detector under two gas mixtures. That deserves credit. The paper is also admirably upfront that high-rate tests are still pending and that the large prototype is not itself the high-rate design.

The main soft spot is the one the stress-test note points at: the >90% efficiency claim is under-specified. Section 4 lists real inefficiencies (the ~20 mm HV-dead band, the four dust spots, the 20 mm periodic HV-gap structure), and Figure 6 has no error bars. The text never says whether the efficiency denominator includes tracks crossing those regions. If it includes them, the quoted number is lower than the local efficiency; if it masks them, then the number applies to a subset rather than the whole active area. Either way, the reader cannot reproduce the number. The text also quotes U and V efficiencies separately and uses the generic phrase ">90% efficiency" in the summary, while the curve that matters for two-dimensional tracking is the U-and-V coincident cluster efficiency, which is the lowest curve in Fig. 6 and is not quoted. That is a substantive quantitative gap, not a nitpick.

The second thing I agree with the reader about: the high-rate motivation is untested here, but the authors say so themselves (Section 5, tests in early 2025). That is a limitation, not a sleight.

The reference list and citation pattern are fine; the self-citations are to their own prior μRWELL paper and LOIs, and none of those are doing load-bearing work. No fitting, no free parameters, no circularity. What you see is a measurement report.

So: does it deserve a referee? Yes. Proceedings papers like this are the normal way detector R&D gets on the record, and the dataset is genuinely new. But I would not take the >90% claim at face value until the authors state the normalization, add error bars or at least a clear binomially-counted efficiency definition, and quote the U-and-V cluster number. A careful referee can get that fixed quickly.

Referee Report

4 major / 4 minor

Summary. This proceedings paper reports R&D progress on Micro-Resistive Well (muRWELL) detectors at Jefferson Lab for future high-luminosity experiments (CLAS12 and SOLID upgrades). The authors describe four 10x10 cm prototypes with varying PEP-dot grounding pitch, readout layout, and well pitch, intended for operation at rates above 1 MHz/cm^2, and a large trapezoidal prototype (145 cm base, 50 cm height) claimed to be the largest muRWELL built to date. Cosmic-ray tests on the large prototype are presented: occupancy maps reveal a dead band, dust-induced inefficient spots, and periodic gaps between HV sections, and efficiency versus HV curves are shown for two gas mixtures, Ar/CO2 80:20 and Ar/Isobutane 90:10. The text claims >90% efficiency for U and V strips with both mixtures, but notes instability with Ar/CO2 and discharges with Ar/Isobutane at 500 V. High-rate beam tests are planned for early 2025 and are not reported in this manuscript.

Significance. If the reported efficiency and stability results are confirmed, this work is a useful step toward using muRWELL technology in high-luminosity tracking detectors. The paper is a conference proceedings contribution presenting preliminary but directly measured data, with clear descriptions of the prototype designs and an honest acknowledgment that high-rate validation is still pending. Its main strengths are the explicit design-parameter tables, the direct cosmic-ray measurements, and the identification of known dead regions in the large prototype. The principal limitation, as the authors themselves state, is the absence of any data at the target rate of about 1 MHz/cm^2; the current claims concern only low-rate cosmic tests. For the reported efficiency claim to be load-bearing, the analysis must be documented more rigorously.

major comments (4)

[Section 4, Fig. 6, Section 5] The central claim of >90% efficiency is not well-defined because the paper never states how the known dead regions are treated in the efficiency denominator. Section 4 documents a ~20 mm wide dead band (HV issue), four dust-related low-occupancy spots, and a periodic 20 mm structure from gaps between HV sections. If these regions are included in the denominator, the dead band alone removes roughly 1.6% of the active area, and the gaps and spots add further losses; if they are excluded, the quoted >90% applies only to a subset of the detector and is not a true full-detector tracking efficiency. Please specify the exact geometric acceptance used in the efficiency calculation, and report efficiencies both with and without masking of the known defective regions.
[Section 4, Fig. 6] The efficiency extraction method is not documented. The paper provides no error bars on the efficiency points, no number of cosmic tracks, no track-selection criteria (e.g., how reference tracks are formed from the GEM telescopes), no cluster-matching definition, and no threshold for what constitutes a hit. Without this information the reader cannot judge whether the observed differences between U and V layers are statistically significant or whether the plateaus are compatible with the quoted 90%. Please add a detailed description of the analysis chain and include statistical uncertainties on all efficiency points.
[Section 4, Fig. 6 and Section 5] The text quotes '>90% efficiency for both U and V strips', but Fig. 6 shows four efficiency curves, including 'Any Cluster' and 'U and V Cluster'. The two-dimensional tracking efficiency, defined as a hit present in both U and V layers, is the lowest curve in the figure and is never quoted in the text or summary. For a real tracking detector, the coincident U-and-V efficiency is the relevant quantity for position measurement. Please report this value explicitly and discuss its magnitude; from the figure it appears to lie below 90% at the nominal operating voltages, which would weaken the summary statement.
[Section 4, stability discussion] The stability comparison between the two gas mixtures is qualitative: the Ar/CO2 data show 'frequent spikes in leakage current', while Ar/Isobutane shows '1-2 discharges per hour' at 500 V. For a detector proposed for high-luminosity tracking, the discharge rate and its effect on the efficiency measurement must be quantified. In particular, state whether the efficiency points were taken during periods free of such spikes, what fraction of running time was affected, and whether any data were rejected because of instabilities.

minor comments (4)

[Introduction, Eq. in paragraph 1] The luminosity unit is written as '10^37 cm^-2 s^-2' in the introduction (Section 1) and in the abstract as 'cm^-2 s^-1'; the correct unit is cm^-2 s^-1. Please correct the inconsistency.
[Section 4, bullet 1] The dead band is described as 'x around in (410 cm - 430 cm)' but the figures use millimeter axes; this should presumably be '410 mm to 430 mm'.
[Section 4, first paragraph] The claim that this is 'the largest muRWELL detector built so far' is not supported by a reference. If this is the authors' own assessment, it should be stated with a comparison to known previous large-area muRWELL constructions or else attributed to a source.
[References] Reference [13] is an internal JLab wiki page; please check that this is accessible to the community or provide a more permanent reference, as the proceedings will be read by those outside JLab.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity; the efficiency results are direct measurements and self-citations are contextual only.

full rationale

This proceeding reports direct measurements of detector performance. The central claim, reaching >90% efficiency for the large μRWELL prototype with Ar/CO2 and Ar/Isobutane mixtures, is obtained from cosmic-ray test data and presented as efficiency-versus-HV curves in Fig. 6. No parameter is fitted to a subset of the data and then used to predict a closely related quantity; no equation is derived from an input that already contains the output. The paper's self-citations (refs. [3], [4] for LOIs, ref. [7] for prior μRWELL measurements, and ref. [13] for context on the CLAS12 luminosity upgrade) are motivational or contextual and are not used as evidence for the measured efficiency values. The authors also explicitly record the main limitation, namely that high-rate capability tests are planned for early 2025, which means the high-luminosity suitability claim is an extrapolation rather than a circular result. Concerns about the efficiency denominator and dead-region treatment noted in the skeptic analysis are experimental-reporting issues, not circularity. Therefore the derivation chain, such as it is, is self-contained with respect to circularity.

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

No parameters are fitted to data in this paper. Detector geometry settings (PEP-dot pitch, well pitch, readout pitch) are design choices, and HV and drift field are operating conditions, not fitted to support a derivation. No new physical entities are introduced; the μRWELL and PEP-dot structures are prior technology from the cited literature.

assumptions (3)

domain assumption The cosmic-ray test stand with two GEM reference trackers and scintillator triggers yields an unbiased estimate of μRWELL efficiency.
Sec. 3 describes the setup but gives no information on track selection or matching cuts; if the reference trackers or trigger bias the sample, the quoted efficiencies change.
domain assumption Cosmic-test efficiency and stability at low rate are representative of performance at the target rate near 1 MHz/cm2.
The paper's motivation is high-rate operation, but only cosmic data are shown; Sec. 5 states high-rate beam tests are planned for early 2025.
ad hoc to paper The observed dead regions (HV gap, dust spots) do not materially affect the reported average efficiency.
Sec. 4 describes a 20 mm dead band and four dust spots but does not state whether these regions are excluded from the efficiency denominator.

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Pith. "Pith review of uRWELL detector developments at Jefferson Lab for high luminosity experiments." pith.science (2026). https://pith.science/paper/UPVBYK7B

@misc{pith2026241113734,
  author       = {Pith},
  title        = {Pith review of: uRWELL detector developments at Jefferson Lab for high luminosity experiments},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/UPVBYK7B}},
  note         = {Machine review of arXiv:2411.13734}
}

abstract

One of the future plans at Jefferson Lab is running electron scattering experiments with large acceptance detectors at luminosities $> 10^{37}cm^{-2}s^{-1}$. These experiments allow the measurements of the Double Deeply Virtual Compton Scattering (DDVCS) reaction, an important physics process in the formalism of Generalized Parton Distributions, which has never been measured because of its small cross-section. The luminosity upgrade of CLAS12 or the SOLID detector makes Jefferson Lab a unique place to measure DDVCS. One of the important components of these high luminosity detectors is a tracking system that can withstand high rates of $\approx 1MHz/cm^{2}$. The recently developed Micro-Resistive Well (uRWELL) detector technology is a promising option for such a tracking detector by combining good position resolutions, low material budget with simple mechanical construction, and low production costs. In this proceeding, we will discuss recent developments and studies with uRWELL detectors at Jefferson Lab for future upgrades of the CLAS12 detector to study the DDVCS reaction.

Figures

Figures reproduced from arXiv: 2411.13734 by the authors.

**Figure 1.** (Left) Schematic drawing of a 𝜇-RWELL detector [9]. (Right) PEP-dot structure in a 𝜇-RWELL detector for charge evacuation [12]. the ground, which depends on the particle’s point of incidence, introduces limitations on the rate capability of the detector. During the past several years, various R&Ds on high-rate layouts [8] were tested, and recently introduced PEP (Patterning-Etching-Plating) shows promising results i… view at source ↗

**Figure 2.** (Left) Experimental setup for testing of small 𝜇RWELL prototypes with cosmic particles. (Right) View of setup in Geant4 simulations with a particle crossing each detector. The detector test stand is shown in [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗

**Figure 3.** First results from prototype 1 with cosmic particles. ADC distributions for readout planes X (a) and Y (b). (c) 2D hit position map, which show holes from grounding dots. and resolutions on HV settings and different gas mixtures before high-rate beam tests. 4. Large prototype detector for CLAS12 luminosity upgrade We also study large area 𝜇RWELL detector for the CLAS12 forward tracking to support operations at twice… view at source ↗

Figures from the paper (3 more)

**Figure 4.** Figure 4: (Left) Photo of the large 𝜇RWELL prototype detector. (Right) The schematic drawing describing the orientations of readout strips. U strips are represented by a blue solid line, V strips are shown by a red dashed line. Note: In the picture only 4 lines are shown from ea…

**Figure 5.** Figure 5: Distribution of hit coordinates on the detector surface from the cosmic data. (Left) “Y vs X” hit distribution. (Right) X hit distribution in the -85 mm to 85 mm range. 1. The detector has a ∼ 20 mm wide region at x around ∈ (410 cm − 430 cm, with essentially no occupa…

**Figure 6.** Figure 6: Efficiency as a function of HV for Ar:CO2 gas 80:20 mixture (left) and for Ar:C4H10 gas 90:10 mixture (right). Red circle markers represent the U layer efficiency, blue squares represent the V layer efficiency, upright triangles in pink is the efficiency of a hit in an…

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Reference graph

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Pith tools

Reviewed August 12, 2026 · model on record in the stance chip above.

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