High-Efficiency WLS Plastic for a Compact Cherenkov Detector

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript describes experimental studies of a wavelength-shifting plastic, consisting of PMMA with a fluorescent dopant, which can be used to increase the light yield in compact Cherenkov detectors. While the material was developed and presented in a previous paper by the same group, there are some new results included in this work: 1) experimental confirmation of negligible scintillation properties of the material, 2) demonstration of its use alongside a conventional scintillator for a ToF system, as well as a compact non-ToF system capable of 20% resolution velocity measurement.

Therefore, there is a sufficient aspect of novelty in this work, which justifies its publication and should trigger some interest in the community.

Nevertheless, I have several, mostly minor, suggestions/questions, and comments, which could be used to improve the readability and quality of the paper following its minor revision.

Introduction:

I am missing a concise summary of the literature values of parameters of BBT, relevant for WLS and Cherenkov detection, in particular the fluorescence time constant and the quantum efficiency, with literature references. There is a lot of published work, e.g. https://pubs.acs.org/doi/abs/10.1021/jp207136k 

For the photoluminescence quantum efficiency, values between 0.6 (in the reference above) and 0.9 (in C. Brizzolari et al 2021 JINST 16 P09027)  were published - is it possible to tell which one is more consistent with the results presented in this work?

In any case, quoting these values explicitly in a table or in the text would be useful for the reader. 

Is anything known on the temperature dependence of these properties, which is relevant when considering space or liquid argon use, and relying on the room temperature comparison presented here?

Section 2:

Is the electronics and PMT response linear in the signal amplitude range presented in Fig 2 and Fig 3? Please clarify in the text.

line 62: is the statement about following expectations from the Bethe–Bloch formula purely qualitative, or can it be made quantitative?

What fit functions were used to fit the peaks in Fig 2? Was it Landau or Langauss? Please clarify.

It is not clear how the following conclusion is made. "The LYSO test suggests it is up to 30 times lower, while proton-beam data indicate a fraction below 0.3%". Please explain in more detail the analysis that led to it.

Section 3:

line 93: typo "about 8This resolution"

line 132 and Fig 6: it is not clear how the conclusion on "velocity resolution better than 20%". Please provide more details, referring clearly to features in Fig 6. 

Fig 6, right panel:

What are the red contours? 

What is the unit of the Z (colour) scale?

 

 

 

Author Response

We tanks Reviever1 for useful suggestions/comments.

I attach a PDF files with responses.

Thank you

Francesco Nozzoli

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper presents a study of the wavelength-shifting plastic FB118 using ionizing radiation. The material is exposed to cosmic muons, protons, and gamma particles, and its light yield is measured with PMTs. When compared to EJ-200, a popular scintillator, FB118 shows very little scintillation light yield and high yields of Cherenkov radiation. This is concluded after comparing results from cosmic muons and a proton beam. Results from gamma ray sources further corroborate these findings and provide constraints on the residual scintillation yield. Finally, a setup with time-of-flight detection for cosmic muons is used. The results show a clear separation between slow and fast-moving muons and demonstrate that using the Cherenkov signal to estimate the β of the muons is feasible. The development of Cherenkov detectors with high and clean Cherenkov radiation yields is a task of great interest and importance for the particle physics community. These results are certainly interesting and well within the scope of Particles. The manuscript communicates these findings effectively. I am recommending this manuscript for publication. Below, you can find a few more major comments/questions that I have, and then a list of some minor comments and recommendations that I believe will be useful in improving the final publication. 

Major comments

1. Lines 57-61: It’s a bit difficult for me to understand the orientation of the setup from the text and the picture. Is the setup stacked vertically, as shown in the image? I am asking because the muon trajectory is drawn tilted (they can have an angle, of course). Also, what is the proton beam axis? Does it fall at the top of the setup so that it passes all three materials?
2. Lines 129-133: I believe this part needs a better and more detailed explanation. I assume that the Frank-Tamm eq. and the signal amplitude are used to calculate the expected β. Is this correct? Then, is this combined with the ToF measurement? Is this combination that gives a resolution of 20%? Why not show these calculations explicitly?

Minor comments

1. Abstract Line 6: Decapitalize “Wavelength Shifting” → “wavelength shifting”
2. Equation 1: β_thr is not defined in the text. Edit: Now I noticed that it is defined a bit later. I think it should be moved right before or after the first mention.
3. Equation 2: All the new symbols should be defined below the equation.
4. Figure 1: This is more of a personal preference and not a requirement, but maybe leave a gap between figures A and B? The colors are very similar, and having them adjacent is a bit confusing.
5. Figure 2: What are the solid lines in the figure? They look like fits using two-sided Gaussians. Perhaps it should be stated in the caption?
6. Table 1: I would add a line to separate the header from the two other lines.
7. Lines 81-83: I assume this conclusion is made by assuming that higher light yields correspond to scintillation, and then dividing those. Perhaps this should be mentioned explicitly? 
8. Line 93: “... with a resolution of about 8This resolution …” I believe something is missing here.
9. Line 100: Does the “slow particles” mean that they are below β_thr?
10. Figure 6, right: 
11. • I would replace the black color with a more striking one, e.g., bright green or magenta. Also, much thicker lines.
    • I don’t see any mention of what the solid and dashed red lines are. My guess is that they represent some kind of percentile.
    • Are these 2D histograms equivalent to the scatter plots in Figure 5? They look similar but not the same. The fast particle parts look suppressed. At least this is true if the color scale is the particle density (this is how I interpret it; there is no label).

Author Response

We thanks Reviewer2 for useful suggestions.

I attached a PDF file with the responses

Author Response File: Author Response.pdf