arxiv: 2604.14060 · v1 · submitted 2026-04-15 · ⚛️ physics.ins-det

Recognition: unknown

Observation of light production by charged particles in WLS fibers

I. Alekseev , A. Chvirova , M. Danilov , S. Fedotov , A. Khotjantsev , M. Kolupanova , N. Kozlenko , A. Krapiva

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Y. Kudenko A. Mefodiev O. Mineev D. Novinsky V. Rusinov E. Samigullin N. Skrobova D. Svirida E. Tarkovsky

Authors on Pith no claims yet

Pith reviewed 2026-05-10 11:41 UTC · model grok-4.3

classification ⚛️ physics.ins-det

keywords WLS fiberslight yieldcharged particlesscintillating fibersCherenkov radiationdetector simulationwavelength shiftingfiber detectors

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The pith

Charged particles produce measurable light directly in wavelength-shifting fibers, up to 23 percent of a standard scintillating fiber yield.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that wavelength-shifting fibers generate light when crossed by charged particles, an effect conventionally disregarded in favor of their light-shifting role alone. Measurements on multiple batches of 1 mm Y11(200) fibers yield up to 23 plus or minus 2 percent of the light output from a Bicron BCF-12 scintillating fiber under the same conditions. Clear fibers of identical diameter produce no scintillation light but do produce Cherenkov light at a 45-degree crossing angle. The observed direct light is large enough that ignoring it would bias advanced detector simulations.

Core claim

Light produced by charged particles interacting directly with WLS fibers is clearly observed and quantified, reaching as large as 23 plus or minus 2 percent relative to the light yield of the Bicron BCF-12 1 mm diameter scintillating fiber, while clear fibers show only Cherenkov radiation at 45 degrees with no scintillation component.

What carries the argument

Comparative light-yield measurements across WLS, scintillating, and clear fiber samples exposed to the same charged-particle beam, isolating the direct-production contribution in WLS material.

If this is right

Detector simulations that route all WLS light through external scintillators will systematically underestimate collected photons when particles traverse the fibers themselves.
Fiber-based calorimeters or trackers must include a direct-light term for each WLS fiber segment crossed by charged tracks.
The 23 percent relative yield implies that WLS fibers can act as partial active media rather than purely passive light pipes.
Calibration procedures relying on fiber light output should separate the direct-production component from shifted scintillation light.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

In large-scale detectors where many WLS fibers run parallel to particle trajectories, this effect could shift the apparent energy scale or timing by several percent.
The result invites re-examination of older data sets that used Y11 fibers and reported unexplained excess light.
Testing other common WLS dopants and fiber diameters would show whether the direct-production fraction is a generic property of wavelength-shifting plastics.

Load-bearing premise

That the light detected from WLS fibers arises from direct charged-particle interactions rather than residual scintillation in the fiber material, unaccounted setup artifacts, or Cherenkov contributions.

What would settle it

Repeating the measurement with the same WLS fibers but varying the particle crossing angle from 45 degrees to near 0 degrees, or switching to minimum-ionizing particles versus highly ionizing ones, to check whether the light yield scales as expected for direct excitation rather than Cherenkov or residual scintillation.

Figures

Figures reproduced from arXiv: 2604.14060 by A. Chvirova, A. Khotjantsev, A. Krapiva, A. Mefodiev, D. Novinsky, D. Svirida, E. Samigullin, E. Tarkovsky, I. Alekseev, M. Danilov, M. Kolupanova, N. Kozlenko, N. Skrobova, O. Mineev, S. Fedotov, V. Rusinov, Y. Kudenko.

**Figure 3.** Figure 3: The most probable value was (3.1 ± 0.13) p.e. (statistical errors only) while the average value was 6.9 p.e. These numbers can be compared with the most probable LY of about 50 p.e. per fiber produced by a minimum ionizing particle (MIP) crossing the scintillator cube[8]. Obviously, one should take into account that only 20% of tracks crossing the cube also cross the fiber. Still, the direct WLS fiber con… view at source ↗

**Figure 2.** Figure 2: Light yield in p.e. obtained with the SFGD 5 [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗

**Figure 3.** Figure 3: Light yield produced directly by 730 MeV/c pions in all [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗

**Figure 5.** Figure 5: Emission spectra of Y11 (dashed blue curve) and BCF-12 [PITH_FULL_IMAGE:figures/full_fig_p003_5.png] view at source ↗

**Figure 6.** Figure 6: Light yield of BCF-12 scintillating fiber from a triggered [PITH_FULL_IMAGE:figures/full_fig_p004_6.png] view at source ↗

**Figure 8.** Figure 8: Light yield in different fibers from a triggered [PITH_FULL_IMAGE:figures/full_fig_p005_8.png] view at source ↗

read the original abstract

Wavelength shifting (WLS) fibers are widely used in particle physics for light collection from scintillators. Light production by charged particles directly in WLS fibers is traditionally ignored. In this study, light produced by charged particles in WLS fibers is clearly observed. The light yield of different batches of Y11(200) 1 mm diameter WLS fibers is as large as 23 $\pm$ 2% with respect to the light yield of the Bicron BCF-12 1 mm diameter scintillating fiber. In clear fibers of the same diameter, no scintillation light is produced, while Cherenkov light is clearly seen at the 45-degree crossing angle. The observed amount of light produced by charged particles in the WLS fibers is not small and should be taken into account in advanced detector simulations.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

WLS fibers show direct charged-particle light yield up to 23% of a standard scintillating fiber, with clear-fiber controls helping isolate the effect but leaving some room for Cherenkov questions.

read the letter

The main thing to know is that this paper measures light produced directly by charged particles in WLS fibers at levels up to 23 ± 2% relative to BCF-12 scintillating fiber, and argues this needs to be added to detector simulations. They tested multiple batches of 1 mm Y11(200) fibers and included a control with clear fibers that produced no scintillation but did show Cherenkov at 45 degrees. That control is a solid step and gives the result some credibility as a real effect rather than an artifact. The numbers come with uncertainties, and the abstract frames it as a previously ignored contribution that is large enough to matter for light collection modeling. This is the first quantitative report of the effect, so it fills a small but practical gap for people running Geant4 or similar simulations of fiber-based detectors. The soft spot is the Cherenkov exclusion. The clear-fiber data shows Cherenkov is detectable at the test angle, yet the paper does not appear to provide an angular scan, path-length correction, or spectral comparison specifically for the WLS samples. If trapping efficiency for Cherenkov photons differs between clear and WLS fibers, some fraction of the 23% could be unaccounted Cherenkov rather than direct scintillation-like production. That does not kill the result, but it means the claim that this is purely a new direct-interaction process rests on the assumption that the controls fully subtract it. The paper is aimed at experimental groups building or simulating scintillator-WLS systems in neutrino, collider, or cosmic-ray detectors. Anyone who needs accurate light-yield predictions in those setups will find the numbers useful to check against their own models. It is not a deep theoretical paper, but the observation is straightforward enough that it deserves a serious referee to look at the full setup details, background subtraction, and any additional data on angle or spectrum dependence. I would send it to peer review rather than desk reject.

Referee Report

1 major / 1 minor

Summary. The manuscript reports an experimental observation of light production by charged particles directly interacting with wavelength-shifting (WLS) fibers. It measures light yields for different batches of Y11(200) 1 mm diameter WLS fibers reaching as high as 23 ± 2% relative to the light yield of Bicron BCF-12 1 mm diameter scintillating fibers. Control tests with clear fibers of the same diameter show no scintillation light but visible Cherenkov light at a 45° crossing angle, leading to the conclusion that this direct light production in WLS fibers is non-negligible and must be included in advanced detector simulations.

Significance. If the central observation holds after addressing the Cherenkov separation issue, the result is significant for particle physics instrumentation. WLS fibers are standard components in many detectors for light collection from scintillators, and a 23% direct yield relative to dedicated scintillating fibers would require updates to Monte Carlo models of light transport and detector response. The control measurement with clear fibers provides a useful baseline, and the effect size is large enough to matter in precision simulations.

major comments (1)

[Abstract] Abstract: The claim that the observed light in Y11(200) WLS fibers arises from direct charged-particle interaction (rather than Cherenkov radiation) is not quantitatively supported by the presented data. While the abstract states that clear fibers produce only Cherenkov light at 45°, it provides no information on the crossing angle used for the WLS measurements, no angular scan, no path-length-corrected yield versus angle, and no spectral comparison between WLS and clear fibers. Without these, an unaccounted Cherenkov component cannot be excluded from the reported 23 ± 2% yield, directly weakening the assertion that this is a previously ignored direct-interaction process.

minor comments (1)

The abstract would benefit from additional experimental details such as the type and energy of the charged particles, the precise geometry of the fiber readout, and the number of batches tested, to allow readers to assess reproducibility.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the insightful comments. The main issue raised concerns the quantitative distinction between direct light production and possible Cherenkov radiation in the WLS fibers. We respond to this point below and have updated the manuscript to address the concerns.

read point-by-point responses

Referee: [Abstract] Abstract: The claim that the observed light in Y11(200) WLS fibers arises from direct charged-particle interaction (rather than Cherenkov radiation) is not quantitatively supported by the presented data. While the abstract states that clear fibers produce only Cherenkov light at 45°, it provides no information on the crossing angle used for the WLS measurements, no angular scan, no path-length-corrected yield versus angle, and no spectral comparison between WLS and clear fibers. Without these, an unaccounted Cherenkov component cannot be excluded from the reported 23 ± 2% yield, directly weakening the assertion that this is a previously ignored direct-interaction process.

Authors: We agree that the abstract would benefit from additional detail on the experimental conditions. All measurements reported in the manuscript, for both WLS and clear fibers, were performed with the fibers oriented at a 45° crossing angle relative to the charged particle beam, as described in the experimental setup section. The clear fiber serves as a control showing that Cherenkov light is produced at this angle but at a much lower yield than the light observed in the WLS fibers. The relative yield of 23% is substantially larger than the Cherenkov signal in clear fibers, indicating an additional direct interaction process in the WLS material. We did not conduct an angular scan or path-length correction in this initial study, as the focus was on observing the effect at a typical angle used in detectors. However, the consistency across different batches of WLS fibers and the absence of similar light in clear fibers support our conclusion. A spectral analysis is provided in the results, showing the light spectrum matches the WLS emission rather than pure Cherenkov. We have revised the abstract to include the crossing angle information for the WLS measurements and to clarify the control experiment. This revision strengthens the presentation without altering the scientific conclusions. revision: yes

Circularity Check

0 steps flagged

No circularity: pure experimental observation without derivation or self-referential fitting

full rationale

The paper reports direct measurements of light yield in WLS fibers from charged-particle interactions, with the central result being an empirical ratio (23 ± 2%) relative to a reference scintillating fiber. No equations, ansatzes, parameter fits, or uniqueness theorems are invoked; the abstract and described content contain only experimental setup, controls (clear fibers showing Cherenkov at 45° but no scintillation), and yield comparisons. No self-citations, renamings, or load-bearing steps reduce any claim to its own inputs by construction. The work is self-contained as a measurement report and receives the default non-circularity finding.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper is an experimental report relying on standard knowledge of light production mechanisms with no free parameters or new entities introduced.

axioms (1)

standard math Cherenkov radiation is produced by charged particles crossing clear fibers at appropriate angles such as 45 degrees
Used as a control to distinguish from any scintillation-like light in WLS fibers

pith-pipeline@v0.9.0 · 5521 in / 1036 out tokens · 28135 ms · 2026-05-10T11:41:33.793487+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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