REVIEW 4 major objections 5 minor 34 references
Performance Study of a Position-sensitive Plastic Scintillator Detector
T0 review · 4 major / 5 minor · reviewed 2026-08-16 · deepseek-v4-flash
Pith's one-line read The paper claims a flat 200×200×6 mm plastic scintillator with 64 SiPMs can reconstruct simulated muon hits to about 1.5 mm using a CNN trained only on timing data, with 22.29 ps timing resolution.
desk verdict Simulation-only design study with a new geometry and a flawed geometric reconstruction; the headline numbers are simulation outputs, not measured performance, but the work is coherent and deserves 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 mechanism that carries the argument is the spatial encoding of photon arrival times. Photons created at the muon track reach nearby SiPMs sooner, so the 64 readout times form a pattern that shifts with hit position, and the detector's fourfold symmetry makes this pattern translationally invariant. The geometric branch uses $L = tc/n$ to turn each arrival time into a circle, pairs the 64 SiPMs to draw 2016 intersecting circles, and locates the hit at the center of the largest circle empty of intersection points. The learning branch reshapes the 64 times into a $(2,16,2)$ tensor that respects the left/right and up/down symmetry and feeds it through two convolutional layers with ReLU, batch normalization, average pooling, and dropout, followed by fully connected regression trained with MSE loss and the Adam optimizer. The timing branch uses a photoelectron-weighted average, Eq. (2), to suppress the strong dependence of single-channel timing on hit position.
What would settle it
Build the described 200×200×6 mm scintillator with 64 edge-coupled SiPMs, send a collimated source or scanned beam to known positions, and apply the same weighted-time and CNN algorithms: measured residuals far from 1.5 mm, or a time spread far from 22.29 ps, would falsify the central claim. A faster check is to measure the actual single-photoelectron waveform and transit-time jitter and rerun the simulation with those measured inputs; if the predicted resolution degrades to match the measurement, the simulation assumptions are the identified cause.
Extended reading notes
Core claim
The central claim is that the timing pattern across the 64 edge-mounted SiPMs contains enough spatial information to localize a hit well below the detector's 200 mm scale. The paper shows that a CNN trained to regress hit coordinates from the per-channel times reconstructs both coordinates with about 1.5 mm resolution, roughly twice as good as a geometric algorithm that converts arrival-time differences into intersecting circles and finds the largest empty circle. The paper also claims that a photoelectron-weighted average of the 64 channel times removes position-dependent timing jitter and yields a single-peaked arrival-time distribution with 22.29 ps resolution. These results are presented as simulation outcomes, demonstrating that a bare scintillator with symmetric SiPM readout can combine fast timing with precise position in one simple structure.
Load-bearing premise
The whole case rests on the GEANT4 simulation faithfully representing the real detector; if the simulated optical surfaces, SiPM photon detection efficiency, transit-time jitter, or electronic noise are optimistic, the measured position and timing resolutions will be worse than the reported 1.5 mm and 22.29 ps.
Editorial extensions
If this is right
- A detector of this geometry could act as a beam-position monitor with millimeter-level accuracy while avoiding the mechanical complexity of slotted scintillators and fiber readout.
- Because the CNN uses only timing information, position reconstruction could in principle proceed without precise per-channel gain or charge calibration.
- The 22.29 ps weighted-average timing resolution would allow the same panel to serve as a time-of-flight counter while simultaneously reporting hit position.
- The two reconstruction methods cross-check each other: the geometric result anchors the interpretation, and the CNN improvement quantifies the nonlinear information available in the timing pattern.
Reading between the lines
- The 1.5 mm figure is a simulation ceiling; dark counts, crosstalk, imperfect optical coupling, and electronic noise will add real-world position jitter, so the measured resolution should be expected to be somewhat worse until the simulation is tuned to bench data.
- The CNN may be fitting simulation-specific artifacts such as the assumed 20 ps transit-time spread and idealized optical surfaces, so transfer to a real detector may require retraining on measured waveforms or domain adaptation.
- Following the paper's own suggestions, adding photoelectron count or pulse amplitude as extra input channels, or replacing the largest-empty-circle fit with Hough circle detection, are natural next steps that should improve both methods.
- The paper's motivating application demands better than 1 mm, so the simulated 1.5 mm result does not yet meet that target; the contribution is evidence that the compact geometry is in the right regime, with the final push left to further algorithms or hardware refinements.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper presents a simulation study of a position-sensitive plastic scintillator detector consisting of a 200 mm × 200 mm × 6 mm EJ-200 scintillator read out by 64 SiPMs arranged on its four sides. Using GEANT4 simulations of 3 GeV/c muons, the authors simulate optical photon transport, synthesize SiPM waveforms from individual photoelectron responses, and extract channel times with a constant-fraction discriminator. They report a weighted-average time resolution of 22.29 ps (Section 3), a geometric reconstruction based on circle intersections and a "largest empty circle" search with roughly 3.4 mm resolution (Section 4.1), and a CNN regressor trained on simulated timing data that achieves approximately 1.5 mm resolution in both horizontal and vertical directions (Section 4.2). The paper concludes that the design provides millimeter-level spatial resolution and sub-30 ps timing performance.
Significance. If the claimed performance were demonstrated on a physical detector, the design would be a compact, low-cost option for beam position monitoring at facilities like XiPAF. The manuscript gives a concrete geometry, a clear simulation chain, and enough detail to reproduce the simulation setup, which is a positive feature. However, the significance is strongly limited by the fact that all headline results are single-point outputs of an unvalidated simulation; no experimental data, benchmark comparison, or uncertainty quantification is provided. In addition, the geometric algorithm in Section 4.1 contains an internal inconsistency, and the CNN evaluation in Section 4.2 measures only the network's ability to reproduce the simulation's mapping rather than the detector's physical resolution. The paper is best read as a preliminary simulation study, not as a demonstration of achieved detector performance.
major comments (4)
- [Section 4.1, Eq. (3)] The geometric reconstruction converts photon arrival times into straight-line distances using L = tc/n, assuming line-of-sight propagation. This directly contradicts the same subsection's statement that "the vast majority undergo multiple reflections within the scintillator." Since the arrival time is dominated by multiply-reflected paths, Eq. (3) does not measure the distance from the emission point to the SiPM, and the circle-intersection construction in Figs. 8-11 is therefore built on an invalid premise. The 3.4 mm resolution claim and Table 1 results are not supported by a consistent physical model.
- [Section 4.2, Figs. 15-16] The reported ~1.5 mm CNN position resolution is obtained by training the network on GEANT4-simulated timing data with simulated truth labels and then evaluating on the same simulation model. This is a self-consistency check of the network's ability to fit the simulation's input-output mapping; it provides no evidence about performance on a physical detector. A meaningful resolution claim would require experimental data, or at minimum a demonstration that the simulation reproduces measured quantities and an estimate of the simulation-to-reality domain gap.
- [Section 2.2 and all results] Every headline number (22.29 ps in Section 3, ~3.4 mm in Section 4.1, ~1.5 mm in Section 4.2) depends on an unvalidated simulation chain: GEANT4 optical transport, the SPE waveform superposition of Eq. (1), CFD timing, and the CNN training. The manuscript provides no comparison of simulated NPE spectra, waveform shapes, or timing distributions to any measurement, no benchmark against a known detector, and no uncertainty analysis on critical optical parameters such as the EJ-200 refractive index, surface treatment, or SiPM PDE. Without such validation, the results are assumption-laden simulation outputs and cannot be presented as achieved detector performance.
- [Section 3, Fig. 6] The 22.29 ps time resolution is presented as a single Gaussian fit to a simulated distribution, but the paper does not state the number of simulated events, the fit range, or the statistical uncertainty on the resolution. In addition, the claim that the SiPM transit-time spread (standard deviation 20 ps) "does not affect the outcome" is not justified, which is concerning for a result whose central quantity is a time resolution. The paper should provide the statistical and systematic uncertainty on the quoted value.
minor comments (5)
- [Section 2.1 and Ref. [16]] The text specifies an S13360-6025PE SiPM, but the cited reference [16] links to the S13360-3025PE model. The authors should verify which model is used and correct the reference or the text accordingly.
- [Table 1] The table header contains a stray "/2" and the column labels are poorly formatted, making the table harder to read than necessary.
- [Section 4.1] The largest-empty-circle algorithm depends on an unspecified square search-region side length and a 200×200 grid resolution; these parameters affect the reconstructed positions in Table 1 and Figs. 10-13 and should be stated explicitly.
- [Abstract and Section 5] The wording "a position resolution of mm level has been achieved" and "delivering exceptional temporal sensitivity" overstates results that are purely simulated. The paper should consistently refer to simulated performance until experimental validation is available.
- [Throughout] There are several minor grammatical and typographical errors, e.g., "timimg" in Section 3, "Relation" instead of "Equation" for Eq. (1), and inconsistent use of "SiPM" versus "SiPMs." A careful proofread is needed.
Circularity Check
No circular derivation: the simulated timing, geometric, and CNN results are computed from the stated simulation chain rather than returned as inputs by construction; the one self-citation is not load-bearing.
full rationale
Neither headline number reduces to its own input by construction. The 22.29 ps timing resolution is obtained by applying Eq. (2), an NPE-weighted average, to simulated per-channel timestamps and Gaussian-fitting the resulting distribution; no fitted parameter is renamed as a prediction. The CNN result is a supervised regression: the inputs are GEANT4-simulated SiPM timing features and the labels are the same simulation's true hit positions. Evaluating the trained network on validation data measures how well the simulated timing features encode position; that is a consistency/interpolation benchmark, not a quantity forced to equal the label by definition. The geometric algorithm does combine simulated times with Eq. (3) L = tc/n, but Eq. (3) is an assumed straight-line propagation model, and the reconstruction output is the fitted blank-region center, which is not algebraically identical to the timing inputs. The paper's own admission that most detected photons undergo multiple reflections is a modeling inconsistency and a simulation-fidelity concern, not a circular reduction. The only self-citation, ref. [20] from overlapping authors on a prior T0 detector, motivates the averaging strategy, but the present numerical timing result is recomputed in this paper's own simulation, so the citation is not load-bearing for the 22.29 ps claim. No uniqueness theorem, ansatz, or external constraint is imported from the authors' prior work. The central vulnerability is external validity: all performance numbers are simulation-only and are not benchmarked against a measurement, an uncertainty analysis, or released code and data. That is a correctness and validation risk, but it is not circularity under the required definition.
Assumptions & free parameters
free parameters (5)
- Search region side length for the largest empty circle algorithm
- Search grid resolution =
200x200
- Constant fraction discriminator threshold =
20%
- CNN early stopping patience =
2000 epochs
- SiPM transit time jitter sigma =
20 ps
assumptions (4)
- domain assumption The GEANT4 simulation faithfully models the detector's optical and electronic response.
- domain assumption 3 GeV/c muons are minimum ionizing particles and are incident uniformly and perpendicularly.
- domain assumption The refractive index of the scintillator is 1.58 and the speed of light in the material is c/n for time-to-distance conversion.
- domain assumption The SiPM dark count, crosstalk, and afterpulsing are not included in the digitization.
Cite this review
Pith. "Pith review of Performance Study of a Position-sensitive Plastic Scintillator Detector." pith.science (2026). https://pith.science/paper/DL5VA2ES
@misc{pith2026250419083,
author = {Pith},
title = {Pith review of: Performance Study of a Position-sensitive Plastic Scintillator Detector},
year = {2026},
howpublished = {\url{https://pith.science/paper/DL5VA2ES}},
note = {Machine review of arXiv:2504.19083}
}
read the original abstract
For a long time, scintillator detectors have suffered from relatively weak spatial resolution due to various influencing factors. Additionally, the high cost of photomultiplier tubes (PMTs) has limited the widespread adoption of scintillator detectors as position-sensitive detectors in particle and nuclear physics experiments. In recent years, thanks to the rapid development of silicon photomultipliers (SiPMs), their excellent cost-performance ratio has led to a renewed interest in scintillator detectors in particle and nuclear physics. This project provides a detailed discussion of a detector based on scintillators coupled with SiPMs, focusing on how to improve the detector's position accuracy. By developing algorithms based on traditional optical propagation, a position resolution of mm level has been achieved. Furthermore, the introduction of a machine learning CNN algorithm has further enhanced the detector's position resolution.
Figures
Figures from the paper (13 more)
Reference graph
Works this paper leans on
-
[1]
Yue,C.B., Ma,P.F, Wang,B.C., et al. Beam dynamics design of a proton/heavy-ion injector for the synchrotron of the Xi- PAF upgrading project[J]. Nuclear Instruments and Meth- ods in Physics Research Section A: Accelerators, Spectrom- eters, Detectors and Associated Equipment, 2025: 170537. doi:10.1016/j.nima.2025.170537
-
[2]
Wang,Z.M., Chen,W., Qiu,M.T., et al. Construction and beam commissioning of a compact proton synchrotron for space radiation environment simulation[J]. Nuclear Instru- ments and Methods in Physics Research Section A: Acceler- 33 ators, Spectrometers, Detectors and Associated Equipment, 2022,1027:166283. doi:10.1016/j.nima.2021.166283
arXiv 2022
-
[3]
Plastic scintil- lation detectors for time-of-flight mass measurements[J]
Wang,K., Estrade,A., Neupane,S., et al. Plastic scintil- lation detectors for time-of-flight mass measurements[J]. Nuclear Instruments and Methods in Physics Re- search Section A: Accelerators, Spectrometers, Detec- tors and Associated Equipment, 2020, 974: 164199. doi:10.1016/j.nima.2020.164199
-
[4]
Reaching time res- olution of less than 10 ps with plastic scintillation de- tectors[J]
Zhao,J.W., Sun,B.H., Tanihata,I., et al. Reaching time res- olution of less than 10 ps with plastic scintillation de- tectors[J]. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, De- tectors and Associated Equipment, 2016, 823: 41-46. doi:10.1016/j.nima.2016.03.106
-
[5]
Design of a high dynamic range photomultiplier base board for the BGO ECAL of DAMPE[J]
Zhang,Z., Zhang,Y., Dong,J., et al. Design of a high dynamic range photomultiplier base board for the BGO ECAL of DAMPE[J]. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrome- ters, Detectors and Associated Equipment, 2015, 780: 21-
work page 2015
-
[6]
Study on the optimized 34 energy resolution of scintillator detectors based on SiPMs and LYSO: Ce[J]
Hu,P., Hua,Z.H., Ma,L.S., et al. Study on the optimized 34 energy resolution of scintillator detectors based on SiPMs and LYSO: Ce[J]. Journal of Instrumentation, 2022, 17(09): T09010. doi:10.1088/1748-0221/17/09/T09010
-
[7]
Bravar,U., Bruillard,P.J., Flckiger,E.O., et al. Design and testing of a position-sensitive plastic scintilla- tor detector for fast neutron imaging[J]. IEEE trans- actions on nuclear science, 2006, 53(6): 3894-3903. doi:10.1109/TNS.2006.886046
-
[8]
Song,S., Kim,J., Park,J.H., et al. High-spatial-resolution position-sensitive plastic scintillation optical fiber bun- dle detector[C]//Photonics. MDPI, 2021, 8(2): 26. doi:10.3390/photonics8020026
Show all 34 references
-
[9]
Anode position and last dynode timing circuits for dual-layer BGO scintilla- tor with PS-PMT based modular PET detectors[J]
Zhang,N., Thompson,C.J., Togane,D., et al. Anode position and last dynode timing circuits for dual-layer BGO scintilla- tor with PS-PMT based modular PET detectors[J]. IEEE Transactions on Nuclear Science, 2002, 49(5): 2203-2207. doi:10.1109/TNS.2002.803815
2002
-
[10]
Sub-3mm spatial resolution from a large monolithic LaBr3 (Ce) scin- tillator[J]
Liprandi,S., Mayerhofer,M., Aldawood,S., et al. Sub-3mm spatial resolution from a large monolithic LaBr3 (Ce) scin- tillator[J]. Current Directions in Biomedical Engineering, 2017, 3(2): 655-659. doi:10.1515/cdbme-2017-0138. 35
2017 doi
-
[11]
LAL Orsay, 2012
Collazuol,G., The sipm physics and technology-a review[J]. LAL Orsay, 2012
2012
-
[12]
Development of a muon detector based on a plastic scintillator and WLS fibers to be used for muon tomography system[J]
Park,C., Kim,K.B., Baek,M.K., et al. Development of a muon detector based on a plastic scintillator and WLS fibers to be used for muon tomography system[J]. Nu- clear Engineering and Technology, 2023, 55(3): 1009-1014. doi:10.1016/j.net.2022.11.016
2023 doi
-
[13]
A cosmic ray imaging sys- tem based on plastic scintillator detector with SiPM read- out[J]
Liang,Z., Hu,T., Li,X., et al. A cosmic ray imaging sys- tem based on plastic scintillator detector with SiPM read- out[J]. Journal of Instrumentation, 2020, 15(07): C07033. doi:10.1088/1748-0221/15/07/C07033
2020 doi
-
[14]
https://eljentechnology.com/products/plastic- scintillators/ej-200-ej-204-ej-208-ej-212
-
[15]
IEEE Transactions on Nuclear Science, 2015, 62(5): 1972-
ter Weele,D.N., Schaart,D.R., Dorenbos,P., Scintillation de- tector timing resolution; a study by ray tracing software[J]. IEEE Transactions on Nuclear Science, 2015, 62(5): 1972-
2015
-
[16]
https://www.hamamatsu.com/us/en/product/optical- sensors/mppc/S13360-3025PE.html
-
[17]
GEANT4—a 36 simulation toolkit[J]
Agostinelli,S., Allison,J., Amako,K., et al. GEANT4—a 36 simulation toolkit[J]. Nuclear instruments and methods in physics research section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003, 506(3): 250-
2003
-
[18]
Geant4 developments and applications[J]
Allison,J., Amako,K., Apostolakis,J.E.A., et al. Geant4 developments and applications[J]. IEEE Transac- tions on nuclear science, 2006, 53(1): 270-278. doi:10.1109/TNS.2006.869826
2006
-
[19]
CDF Note 5358, 2000
Jones,M., PMT base design for the CDF-II time-of-flight system[R]. CDF Note 5358, 2000
2000
-
[20]
Design and performance testing of a T0 detector for the CSR External-target Ex- periment[J]
Hu,D., Wang,X., Shao,M., et al. Design and performance testing of a T0 detector for the CSR External-target Ex- periment[J]. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detec- tors and Associated Equipment, 2023, 1057: 168773. do...
2023
-
[22]
Improved calorimetric particle identification in NA62 using machine learning techniques[J]
Cortina Gil,E., Kleimenova, A., Minucci, E., et al. Improved calorimetric particle identification in NA62 using machine learning techniques[J]. Journal of High Energy Physics, 2023, 2023(11): 1-15. doi:10.1007/JHEP11(2023)138
2023 doi
-
[23]
Machine learning method for 12C event classification and reconstruction in the active target time-projection chamber[J]
Wu,H., Wang, Y., Wang, Y., et al. Machine learning method for 12C event classification and reconstruction in the active target time-projection chamber[J]. Nuclear In- struments and Methods in Physics Research Section A: Ac- celerators, Spectrometers, Detectors and Associated E...
2023
-
[24]
NATURE COMMUNICATIONS, 2025, 16(1).doi:10.1038/s41467- 024-55042-y
Bianchi,F., Observation of a rare beta decay of the charmed baryon with a Graph Neural Network[J]. NATURE COMMUNICATIONS, 2025, 16(1).doi:10.1038/s41467- 024-55042-y
2025 doi
-
[25]
Measurements of decay branch- ing fractions of the Higgs boson to hadronic final states at the CEPC[J]
Ma,X., Wu,Z., Wu,J., et al. Measurements of decay branch- ing fractions of the Higgs boson to hadronic final states at the CEPC[J]. Chinese Physics C, 2025. doi:10.1088/1674- 1137/adacc5
2025 doi
-
[26]
doi:10.1016/j.nima.2015.01.036
2015 doi
-
[27]
First appli- cation of machine learning algorithms to the position re- construction in Resistive Silicon Detectors[J]
Siviero,F., Arcidiacono,R., Cartiglia,N., et al. First appli- cation of machine learning algorithms to the position re- construction in Resistive Silicon Detectors[J]. Journal of Instrumentation, 2021, 16(03): P03019. doi:10.1088/1748- 0221/16/03/P03019
2021 doi
-
[28]
Deep learn- ing[M]
Goodfellow,I., Bengio,Y., Courville,A., et al. Deep learn- ing[M]. Cambridge: MIT press, 2016
2016
-
[29]
Using deep neural networks to improve the precision of fast-sampled particle 38 timing detectors[J]
Kocot,M., Misan,K., Avati,V., et al. Using deep neural networks to improve the precision of fast-sampled particle 38 timing detectors[J]. arXiv preprint arXiv:2312.05883, 2023. doi:10.7494/csci.2024.25.1.5784
2023 arXiv
-
[30]
Jour- nalofMachineLearningResearch, 2014, 15(1): 1929
SrivastavaN,H.G., Krizhevsky,A., Dropout: A simple- waytopreventneuralnetworksfromoverfitting[J]. Jour- nalofMachineLearningResearch, 2014, 15(1): 1929. doi:10.5555/2627435.2670313
2014
-
[31]
arXiv preprint arXiv:1609.04747, 2016
Ruder,S., An overview of gradient descent optimiza- tion algorithms[J]. arXiv preprint arXiv:1609.04747, 2016. doi:10.4855-/arXiv.1609.04747. 39
2016 arXiv
-
[32]
pmlr, 2015: 448-456
Ioffe,S., Szegedy,C., Batch normalization: Accelerating deep network training by reducing internal covariate shift[C]//International conference on machine learning. pmlr, 2015: 448-456. doi:10.5555/3045118.3045167
2015
- [35]
-
[303]
doi:10.1016/S0168-9002(03)01368-8
-
[1980]
doi:10.1109/TNS.2015.2460266
2015
Reviewed August 16, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.