Hit-rate capability of a silicon strip detector module for decay positron detection in the J-PARC muon $g-2$/EDM experiment

Hiroshi Sendai; Hiroshi Yamaoka; Hiroyuki A. Torii; Junichi Suzuki; Junji Tojo; Katsunori Awa; Koichiro Shimomura; Maki Sakakibara; Manobu M. Tanaka; Masayoshi Shoji

REVIEW 4 major objections 5 minor 16 references

Hit-rate capability of a silicon strip detector module for decay positron detection in the J-PARC muon $g-2$/EDM experiment

T0 review · 4 major / 5 minor · reviewed 2026-08-02 · deepseek-v4-flash

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Pith's one-line read A silicon strip detector module for the J-PARC muon g-2/EDM experiment loses only about 10% of signal hits due to pileup at the maximum expected per-strip hit rate of 1.4 MHz, a loss the authors argue is negligible for track reconstruction

desk verdict A plausible and genuinely new module-level beam test of the J-PARC quarter-vane detector, but the headline 10% hit-loss number sits on a fit that doesn't fully describe the data and the paper itself defers the needed simulation cross-check. read the letter →

arxiv 2606.16347 v3 pith:LIUWM6CR submitted 2026-06-15 physics.ins-det

Ryuto Azuma , Katsunori Awa , Shunsuke Doi , Yowichi Fujita , Seiso Fukumura , Yu Goto , Ryotaro Honda , Sohtaro Kanda

show 29 more authors

Tetsuichi Kishishita Tatsuya Kume Tsutomu Mibe Yukiharu Murata Shoichiro Nishimura Shinji Ogawa Yuta Okazaki Naohito Saito Maki Sakakibara Osamu Sasaki Taiki Sato Yutaro Sato Yoshiaki Seino Hiroshi Sendai Koichiro Shimomura Shohei Shirabe Masayoshi Shoji Patrick Strasser Taikan Suehara Shiori Sugahara Junichi Suzuki Toshikazu Takatomi Manobu M. Tanaka Junji Tojo Hiroyuki A. Torii Takashi Yamanaka Hiroshi Yamaoka Takayuki Yamazaki Tamaki Yoshioka

This is my paper · ORCID

classification physics.ins-det

keywords siliconstripdetectormuong-2electricdipolemomentpileuplosshit-ratecapabilityJ-PARCpositrondetectionfront-endASIC

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 the development of the smallest functional unit of the silicon strip tracker for the J-PARC muon g−2/EDM experiment and its beam-test evaluation. The detector must find decay positrons on strips that see up to 1.4 million hits per second, and the question is whether analog pileup destroys too many hits. By fitting the observed time spectrum with an exponential decay modified by a hit-rate–proportional loss term, the authors measure a 10% hit loss at the highest expected rate. They argue that this loss is acceptable because a positron track deposits about 50 hits, so losing one in ten leaves enough for robust reconstruction. The conclusion is that the module meets the experiment's performance requirements.

What carries the argument

The measured object is the quarter-vane module: 190 µm-pitch silicon strip sensors read out by SliT128D ASICs that sample comparator outputs at 200 MHz and record time-over-threshold. The analysis uses a model of pileup loss, f(t)=p0(1−p1 e−t/τ)e−t/τ+p2, which assumes the fractional loss is proportional to the instantaneous hit rate, with τ fixed to the muon lifetime. Fitting this to the time distribution of hits in channels with 0–8 hits per event gives the maximum loss p1 as a function of hit rate.

What would settle it

A direct high-rate measurement at 1.4 MHz per strip—using a stronger beam, a laser, or a fast charge-injection pulser—that yields a hit loss outside the 10% value (or a full analog waveform simulation of the SliT128D that disagrees with the fitted p1) would falsify the central claim. The simplest check is whether the loss continues to grow linearly with rate past 0.5 MHz or bends upward.

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Extended reading notes

Core claim

The central claim is that the quarter-vane silicon strip module loses only about 10% of signal hits due to pileup when the instantaneous per-strip hit rate reaches 1.4 MHz, the maximum expected in the J-PARC muon g−2/EDM storage ring. This number comes from fitting the time spectrum of decay positrons with eq. (4.1), where the efficiency-loss parameter p1 increases linearly with the number of hits per event (and therefore with hit rate). Since a full positron track in the momentum range of interest contains roughly 50 hits, a 10% loss has negligible impact on track reconstruction, so the module satisfies the experiment's key requirement.

Load-bearing premise

The analysis assumes the pileup loss is exactly proportional to the instantaneous hit rate and that the underlying decay follows a single exponential with the known muon lifetime; this model does not fully describe the data (fit probability 0.003), and a cross-check against waveform simulation is left for future work.

Editorial extensions

If this is right

If the 10% loss at 1.4 MHz is confirmed, the quarter-vane module meets the hit-rate requirement of the J-PARC muon g−2/EDM experiment.
A 10% hit loss is small enough that track reconstruction efficiency is effectively unchanged for the ~50-hit positron tracks.
The linear loss-versus-rate relation provides a simple correction factor that can be applied to future data to recover lost hits.
The module's demonstrated performance at 0.2–4 MHz per strip indicates the design can be used in other high-rate positron/electron tracking environments.
The measurement sets a quantitative upper bound on pileup loss that the final 40-vane detector can be expected to meet.

Reading between the lines

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

The fit used to extract 10% has a chi-square probability of only 0.003, so the model does not fully capture the data; a waveform-level simulation cross-check, which the authors list as future work, could shift the central value.
The beam test's highest instantaneous rate was ~0.455 MHz (for 1-hit events); the 1.4 MHz point relies on extrapolation to 3 hits/event, so an experiment with a genuinely higher instantaneous rate would directly test the extrapolation.
Because the loss is linear in rate, the dominant limitation is the 75 ns pulse width of the shaping amplifier; reducing it further would push the tolerable rate upward, an avenue the paper does not explore.
Beam-synchronized noise from another beam line's kicker caused interference during the test; the final experiment will need careful shielding to achieve the same noise performance in situ.

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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

The genuinely new thing here is the integrated beam test: a quarter-vane silicon strip module for the J-PARC muon g-2/EDM experiment, with the SliT ASIC readout, tested under real muon beam conditions. Prior papers characterized the sensor and the ASIC separately; this one gives the module-level hit-rate capability and reports about 10% efficiency loss at the design hit rate of 1.4 MHz. That is a useful, plausible number, and the qualitative conclusion that a 10% loss is negligible for track reconstruction with ~50 hits is probably correct.

The paper has real strengths. The setup is relevant: the MuSEUM beamline provides a pulsed, high-intensity muon beam with the right time structure. The authors report noise, ToT calibration, and the pileup analysis is a standard approach applied cleanly. They also show the fit figure with the χ²/ndf, so the data are not hidden.

The soft spots are exactly where the stress-test note lands. Equation (4.1) is an assumed model where the loss is proportional to the instantaneous hit rate. For the key 3-hits/event sample, the fit probability is 0.0028, and calling it “well described” is an overstatement. There is no systematic uncertainty on p1 beyond the statistical fit error, and the paper explicitly says a consistency check against the waveform simulation (Ref. [16]) remains future work. So the 10% figure is not as firm as the abstract suggests. Also, the conversion from hits/event to hit rate carries its own calibration uncertainty that isn’t discussed.

That said, I don’t think the central requirement validation collapses. The data visibly show a few-percent-to-10% loss in the relevant range, and a more careful simulation cross-check is unlikely to change the conclusion by a factor that would make the detector fail. The issue is precision and wording, not likely a wrong answer.

The citation pattern is fine: the prior module papers are legitimate, and this is the natural next step.

This paper deserves a serious referee. It is a real beam test with useful results for anyone building high-rate silicon strip readout, especially for muon g-2/EDM. I would send it to peer review. The revision should address the fit quality, add a systematic uncertainty, and either do the simulation comparison or soften the "well described" claim.

Referee Report

4 major / 5 minor

Summary. The manuscript reports the construction and beam-test characterization of a quarter-vane silicon strip detector module for the J-PARC muon g−2/EDM decay-positron tracker. After describing the sensor, the SliT readout ASIC, and the FPGA-based readout board, it presents measurements of equivalent noise charge, ToT-charge calibration, noise rejection, and hit-rate capability from data taken at the J-PARC MLF H-line with the MuSEUM setup. The central performance claim is that the pileup-induced hit loss is approximately proportional to the instantaneous hit rate and that at the expected maximum rate of 1.4 MHz per strip the loss is 10%, which the authors argue is negligible for the ~50-hit track reconstruction.

Significance. If correct, the result validates a key performance requirement for a central component of the J-PARC muon g−2/EDM experiment. The paper provides useful characterization of the SliT128D readout chain (noise of 0.200 fC, ~75 ns pulse width, ToT response) and extends the previous prototype work from Refs. [7,10] to a produced module. The authors are transparent in reporting raw fit statistics and in explicitly deferring a simulation cross-check, which is a strength. However, the central 10% number currently rests on a fit whose model does not fully describe the data, and no systematic uncertainty is assigned; the conclusion is therefore not yet conclusive.

major comments (4)

[§4.4, Eq. (4.1), Fig. 10] The text states that the time spectrum is 'well described' by Eq. (4.1), but the reported fit for the 3-hits/event sample has χ²/ndf = 312.9/247, p = 0.0028. This is a poor fit: the model—a pure exponential with a loss term strictly proportional to the instantaneous hit rate—does not fully describe the data. Because the maximum efficiency loss p1 is the parameter from which the 10% value is derived, the central claim currently depends on an inadequately validated functional form. Please either improve the model, restrict the fit range, or add a systematic uncertainty that covers the fit residuals.
[§4.4, Eq. (4.1), Fig. 11] No systematic uncertainty is assigned to p1 or to the derived 10% loss at 1.4 MHz. The extracted p1 will depend on the comparator threshold, the ToT>20 ns cut, the choice of the 20 μs fit window, the 400 ns t=0 definition, and the beam-bunch structure. A systematic budget for p1, propagated through the 1.4 MHz interpolation, is needed before the performance requirement can be stated as demonstrated.
[§4.4, last paragraph] The paper explicitly says 'A consistency check of this result remains a future work' regarding comparison with the analog-waveform simulation of Ref. [16]. Given that the conclusion about negligible impact on track reconstruction is driven by this single 10% number, the cross-check, or a comparable validation against the waveform model, is load-bearing rather than optional. Until then, the conclusions should be worded as provisional, and the claim that the module 'satisfies the performance requirements' is premature.
[§4.4, definition of t=0 and Fig. 11] The analysis starts at t=0 defined as 400 ns after the arrival of the second muon bunch, and p1 is the maximum loss at that t=0. The 'maximum hit rate' on the top axis of Fig. 11 is computed from the number of hits/event as N/τ at this same t=0. However, the 1.4 MHz design rate refers to the beginning of data taking near the muon beam orbit. Since the instantaneous rate 400 ns before the analysis start is higher by a factor exp(0.4 μs/2.197 μs) ≈ 1.20 (if the exponential extrapolation is valid), the loss at the true burst peak may be larger than the reported p1. Please clarify the timing convention or add a conservative extrapolation.

minor comments (5)

[§1.3 title and §2.2.1] The subsection title contains a duplicated word: 'Requirements and design of of the tracking detector'. Please correct.
[Fig. 10] The fit-parameter line for p1 appears as '0.00181 ± 0.09671', which looks like the central value and error are interchanged relative to the ~10% value discussed in the text. Please ensure the printed parameter order is unambiguous.
[Fig. 10] The ratio panel is labeled 'Data / eq.(4.2)' but elsewhere 'eq.' is written with a period; use a consistent style. Also, the top panel y-axis label 'Number of hits / event' would be clearer as 'Number of hits / (event · ns)' if the histogram is bin-normalized.
[§4.4] 'the rest muon lifetime' should be 'the muon lifetime at rest' or 'the muon rest-frame lifetime'.
[References] Reference [10] contains a grammatical error in its title: 'from a pulsed a muon beam' should be 'from a pulsed muon beam'.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the 10% hit-loss value is a directly fitted experimental parameter, not a derivative of the conclusion or of a self-citation chain.

full rationale

The paper's central claim is an experimental measurement: the pileup-loss parameter p1 is obtained by fitting the observed time spectrum of hits with Eq. (4.1), and the 10% efficiency loss at 1.4 MHz is read off from the fitted p1 for the 3-hits/event sample. This is an empirical extraction under an explicit model assumption, not a quantity derived from the conclusion it supports. The cited prior work ([7], [10], [16]) concerns the ASIC, sensor prototype, and a simulation cross-check; none of these citations is used to define the measured loss or to force the 10% value, and the paper explicitly defers the simulation-based consistency check to future work rather than invoking it as evidence. The poor fit quality (χ²/ndf = 312.9/247, probability 0.0028) indicates a model-data agreement issue, which is a correctness or systematic-uncertainty concern, not circularity. No equation is equivalent to its inputs by construction, and no fitted parameter is renamed as a prediction. The derivation chain is self-contained with respect to the measured data.

Assumptions & free parameters 4 free parameters · 5 assumptions · 0 invented entities

The central claim rests on one fitted parameter p1 and the assumed rate-proportional pileup model. No new physical entities are introduced.

free parameters (4)

p1 (maximum efficiency loss at t=0) = 0.09671 ± 0.00181 (3 hits/event sample)
Central fitted parameter in Eq. (4.1); the 10% loss claim is this parameter for the sample corresponding to 1.4 MHz.
p0 (normalization) = 21.53 ± 0.02
Nuisance parameter in Eq. (4.1), fitted to the time spectrum.
p2 (pedestal) = 0.0001963 ± 0.0001263
Nuisance parameter in Eq. (4.1), representing constant background.
Comparator threshold = 0.413 MIP
Operating point chosen for the test; affects the absolute hit loss but not the rate scaling.

assumptions (5)

domain assumption Decay positron time spectrum is exponential with muon lifetime τ = 2.1969811 μs.
Used to fit Eq. (4.1) and to convert hits/event to MHz in §4.4. Muonium decay follows the free muon lifetime, but stopped muons in material could contribute small non-exponential components.
ad hoc to paper Pileup loss is proportional to the instantaneous hit rate (Eq. 4.1).
Ansatz introduced in §4.4; not derived from the circuit model. The fit probability (0.0028) suggests it is approximate.
domain assumption MuSEUM beam conditions (pulsed muon beam, krypton gas, 1.7 T) are representative of the hit-rate environment in the g-2 experiment.
The extrapolation from MuSEUM data to the 1.4 MHz g-2 rate relies on this in §1.4 and §4.4.
standard math The number of hits per event in a channel determines its maximum hit rate as Rmax = N / (τ (1 - e^{-T/τ})).
Used in §4.4 to map the top axis in Fig. 11; assumes no other rate-dependent effects change the counting.
domain assumption ToT > 20 ns cut efficiency is independent of hit rate and time.
Applied in §4.3; if pileup shortens ToT, the cut could remove more hits at early times and bias p1.

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Cite this review

Pith. "Pith review of Hit-rate capability of a silicon strip detector module for decay positron detection in the J-PARC muon $g-2$/EDM experiment." pith.science (2026). https://pith.science/paper/LIUWM6CR

@misc{pith2026260616347,
  author       = {Pith},
  title        = {Pith review of: Hit-rate capability of a silicon strip detector module for decay positron detection in the J-PARC muon $g-2$/EDM experiment},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/LIUWM6CR}},
  note         = {Machine review of arXiv:2606.16347}
}

abstract

In the J-PARC muon $g-2$/EDM experiment, a silicon strip detector will be used to detect positrons from muon decays. The detector consists of planes of detector modules arranged radially. The expected maximum hit rate reaches 1.4~MHz per sensor strip, and achieving high detection efficiency even under such hit-rate conditions is a key performance requirement. We have developed the smallest unit of the detector module, and its performance was evaluated using a muon beam at the J-PARC MLF H-line. The specifications of the detector module and the evaluated hit-rate capability are described in this article.

Review history (2 revisions) →

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Reference graph

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Pith tools

Reviewed August 2, 2026 · model on record in the stance chip above.

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Chetri, et al., GPU-based track-finding for the J-PARC muon𝑔−2/EDM experiment, JINST 21 (2026) P01006

H. Chetri, et al., GPU-based track-finding for the J-PARC muon𝑔−2/EDM experiment, JINST 21 (2026) P01006. – 12 –

2026

[2] [1]

D. P. Aguillard, et al., Measurement of the positive muon anomalous magnetic moment to 127 ppb, Phys. Rev. Lett. 135 (2025) 101802

2025

[3] [2]

G. W. Bennett, et al., Final report of the E821 muon anomalous magnetic moment measurement at BNL, Phys. Rev. D 73 (2006) 072003

2006

[4] [3]

Aliberti, et al., The anomalous magnetic moment of the muon in the Standard Model: an update, Physics Reports 1143 (2025) 1–158

R. Aliberti, et al., The anomalous magnetic moment of the muon in the Standard Model: an update, Physics Reports 1143 (2025) 1–158

2025

[5] [4]

G. W. Bennett, et al., Improved limit on the muon electric dipole moment, Phys. Rev. D 80 (2009) 052008

2009

[6] [5]

Adelmann, et al., Search for a muon EDM using the frozen-spin technique (2021)

A. Adelmann, et al., Search for a muon EDM using the frozen-spin technique (2021). arXiv:2102.08838

arXiv 2021

[7] [6]

Abe, et al., A new approach for measuring the muon anomalous magnetic moment and electric dipole moment, Prog

M. Abe, et al., A new approach for measuring the muon anomalous magnetic moment and electric dipole moment, Prog. Theor. Exp. Phys. 2019 (2019) 053C02

2019

[8] [7]

Kishishita, et al., SliT: A strip-sensor readout chip with subnanosecond time walk for the J-PARC muon𝑔−2/EDM experiment, IEEE Trans

T. Kishishita, et al., SliT: A strip-sensor readout chip with subnanosecond time walk for the J-PARC muon𝑔−2/EDM experiment, IEEE Trans. Nucl. Sci. 67 (2020) 2089–2095

2020