Simulation of a SiPM-Based Cherenkov Camera

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a simulation and calibration study of SiPM camera pixels for Cherenkov telescopes. The topic is timely and the simulation chain (dark noise, crosstalk, afterpulsing, saturation) is potentially valuable. However, several key quantitative results are missing and some methodological descriptions are unclear. The abstract is particularly weak and needs a complete rewrite: it fails to convey the real focus of the work and contains language and content issues (for example “a comprehensive simulation its response” should be “a comprehensive simulation of its response”; “Cherenkov observation” should be “Cherenkov light detection”; the claim that the photon detection efficiency at 405 nm was “confirmed” is meaningless without a numerical value or uncertainty). Section 1 is overly didactic and does not clearly explain the specific goals of the paper. Important numerical information is absent throughout the text (e.g. Figures 6–7 show ADC spectra but no χ²/ndf, p-values, or parameter tables). Equation references are inconsistent (Eq. 2.2 and Eq. 5 do not exist) and some statements are questionable (e.g. SiPMs being “less sensitive to temperature variations than PMTs” requires a reference or rephrasing). The manuscript also contains numerous language and formatting issues, including incorrect plurals (SiPM’s, APD’s), inconsistent units (80 nanoseconds vs 80 ns), and typographical errors such as “INFN Naploli”. Several references are incomplete or contain broken links. A major revision is required, including a new abstract, corrected equation references, standardized terminology and units, verification of all references, and addition of quantitative comparisons (PDE values, fit qualities, parameter tables). In its current form the manuscript is far from a stage where a meaningful peer review can be performed, and a thorough major revision is essential before it can be considered for publication.

Comments on the Quality of English Language

The English is understandable but requires extensive editing. There are frequent grammatical errors, awkward phrases, and incorrect technical plurals. Several sentences are cumbersome or ambiguous and should be rewritten for clarity and precision.

Author Response

Comments 1: The abstract is particularly weak and needs a complete rewrite: it fails to convey the real focus of the work and contains language and content issues (for example “a comprehensive simulation its response” should be “a comprehensive simulation of its response”; “Cherenkov observation” should be “Cherenkov light detection”; the claim that the photon detection efficiency at 405 nm was “confirmed” is meaningless without a numerical value or uncertainty).

Response 1: The abstract has been rewritten to highlight that the scope of the work is to present a novel, accurate method to simulate SiPM response by simulating individual APD currents. The measurement of PDE is detailed in a separate work, so the statement about its confirmation has been removed.

Comments 2: Section 1 is overly didactic and does not clearly explain the specific goals of the paper. 

I added the goal of the paper to the beginning of the introduction.

Comments 3: Important numerical information is absent throughout the text (e.g. Figures 6–7 show ADC spectra but no χ²/ndf, p-values, or parameter tables).

I re-ran the fitting and simulations and produced X^2/dof values for the Gaussian mixture fits, as well as an Epps Singleton two sample test comparing the real and simulated ADC distributions. 

Comments 4: Equation references are inconsistent (Eq. 2.2 and Eq. 5 do not exist) 

Fixed

Comments 4:  some statements are questionable (e.g. SiPMs being “less sensitive to temperature variations than PMTs” requires a reference or rephrasing).

I removed this statement.

Comments 5:  The manuscript also contains numerous language and formatting issues, including incorrect plurals (SiPM’s, APD’s), inconsistent units (80 nanoseconds vs 80 ns), and typographical errors such as “INFN Naploli”.

Fixed

Comments 6: Several references are incomplete or contain broken links. 

Fixed

 

Reviewer 2 Report

Comments and Suggestions for Authors

m-minor comment, M-major comment

line 6, M - the temperature sensitivity for SiPM and MPPC like devices are ~ 3% of output amplitude per degree, and only 0.1% for PMT.. this is a false statement (https://hub.hamamatsu.com/us/en/technical-notes/mppc-sipms/how-does-temperature-affect-the-performance-of-an-SiPM.html)

28,m - SiPM’s -> SiPMs .. same error on like 30, 31.. PEs, not PE's... PE's is something belonging to PE, not a plural

49, M - the gain is linear with overvoltage, yes, within small limits though (working region), then the device goes into non-stop breakdown. However, the noise is increasing exponentially with biasing voltage. line 73 - occasionally you mean like 100 kHz or MHz? depending on the temperature and biasing voltage, dark noise can be immense.

75, M - dark counts depend exponentially on voltage. see figure 9 in https://arxiv.org/pdf/0910.4429

note that tests with magnetic field have been done years ago, also radiation hardness, and temperature. https://www.sciencedirect.com/science/article/abs/pii/S0168900205007618

M, general comment. With the high noise, will the MPPC sensitivity be sufficient for the Cherenkov telescope? The Cherenkov light is not the most brightest light source and the MPPC noise will null the ability to analyze the shape of the circle on the detector wall if that is planned. also some description of the cherenkov telescope design should be mentioned somewhere - the MPPC area is small, making the telescope wall lining from them will be expensive and again, something needs to control noise, temperature, calibration, gain, adjust voltage based on those parameters. its not an easy sensor to work with, that's why PMTs are still used, they are robust on multiple environments but are sensitive to B fields. MPPCs are great to be used in high magnetic fields (tested in 10T and higher by I believe some British groups?) and under high radiation dose of MRad delivered in short time.

M - multiple simulations for MPPC already exist. perhaps, an overview of those? comparison of your results with existing results? is your simulation any better, faster, more accurate ?

 

Author Response

Comments 1: the temperature sensitivity for SiPM and MPPC like devices are ~ 3% of output amplitude per degree, and only 0.1% for PMT.. this is a false statement (https://hub.hamamatsu.com/us/en/technical-notes/mppc-sipms/how-does-temperature-affect-the-performance-of-an-SiPM.html)

I omitted this statement. In the discussion I say that future work will simulate the temperature response of the SiPMs.

Comments 2:  SiPM’s -> SiPMs .. same error on like 30, 31.. PEs, not PE's... PE's is something belonging to PE, not a plural

Fixed

Comments 3: the gain is linear with overvoltage, yes, within small limits though (working region), then the device goes into non-stop breakdown. However, the noise is increasing exponentially with biasing voltage. line 73 - occasionally you mean like 100 kHz or MHz? depending on the temperature and biasing voltage, dark noise can be immense.

I mentioned that gain is linear within the working region and cited that region for the Hamamatsu S13361-3050AE-08. I Present both Hamamatsu's stated value for the dark count rate as well as an independent measurement. This is on the order of ~1MHz. I added in the abstract that this work focuses on a model where gain, uncorrelated noise, and correlated noise are all static. In the discussion, I mention that future work will include temperature and over-voltage dependence based on qualifying data.

Comments 4: 75, M - dark counts depend exponentially on voltage. see figure 9 in https://arxiv.org/pdf/0910.4429

According to https://arxiv.org/pdf/1101.1996, the dependence is initially linear, then exponential. Figure 11 in https://arxiv.org/pdf/0910.4429 shows something similar. I clarify that the dependence becomes exponential.

Comments 5: M, general comment. With the high noise, will the MPPC sensitivity be sufficient for the Cherenkov telescope? The Cherenkov light is not the most brightest light source and the MPPC noise will null the ability to analyze the shape of the circle on the detector wall if that is planned. also some description of the cherenkov telescope design should be mentioned somewhere - the MPPC area is small, making the telescope wall lining from them will be expensive and again, something needs to control noise, temperature, calibration, gain, adjust voltage based on those parameters. its not an easy sensor to work with, that's why PMTs are still used, they are robust on multiple environments but are sensitive to B fields. MPPCs are great to be used in high magnetic fields (tested in 10T and higher by I believe some British groups?) and under high radiation dose of MRad delivered in short time.

Cherenkov light from an air shower would be focused by a mirror onto SiPM matrices. I cited the overview of the PBR experiment, but the scope this paper is to talk about the simulation of the SiPMs in isolation.

Comments 6: multiple simulations for MPPC already exist. perhaps, an overview of those? comparison of your results with existing results? is your simulation any better, faster, more accurate ?

I highlight that other simulations do not simulate the interplay between saturation and noise counts and the resulting pulse pile-up current. Other  simulation frameworks can reproduce ADC distributions but not current as a function of time.

Reviewer 3 Report

Comments and Suggestions for Authors

   

A brief summary of the manuscript: 

In this manuscript, the authors summarizes a method to simulate the response of the SiPM to the UV light which is a potential candidate of the component of the Cherenkov detectors. They verified the photon detection efficiency of the Hamamatsu Multi-Pixel Photon Counter (MPPC)  using a test setup in the lab. The simulation of the light detection efficiency of Silicon Photo-Multiplier (SiPM)  will help to reduce the systematic uncertainty in the experimental measurement with the Cherenkov detector that uses the SiPM. 

• Specific comments
•  line number 10-12 "To understand the response of such an instrument in the context of Cherenkov observation, a comprehensive simulation its response to incident light is needed". It is an unclear statement should rephrase it. 
• Through line 87 to 97 How the readout system in your test-setup works please provide bit more information like the triggering scheme you have been using and what is the data though put and clocking frequency and sampling rate of the digitalizer in your readout board. Great if you could add a schematic diagram (desirable).
•  Line- 215, Online link to  the reference -1 is not available
• Did you conduct the photon detection just with a single frequency or have sideband frequencies as well?

 

 

Author Response

Comments 1:  line number 10-12 "To understand the response of such an instrument in the context of Cherenkov observation, a comprehensive simulation its response to incident light is needed". It is an unclear statement should rephrase it. 

The abstract was rewritten to more clearly describe the goals of the paper (simulation of SiPMs).

Comments 2: Through line 87 to 97 How the readout system in your test-setup works please provide bit more information like the triggering scheme you have been using and what is the data though put and clocking frequency and sampling rate of the digitalizer in your readout board. Great if you could add a schematic diagram (desirable).

I clarified that the readback trigger is activated externally at the same time as the input laser. The scope of this work is to describe the simulation chain, so I cited the proceedings which describe the test setup.

Comments 3: Line- 215, Online link to  the reference -1 is not available

Fixed

Comments 4: Did you conduct the photon detection just with a single frequency or have sideband frequencies as well?

It's just the 405nm laser, described in more detail in the cited work by the Naples group. The scope of this work is just the simulation. 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revised manuscript shows noticeable improvements with respect to the previous version. Nevertheless, the text still requires thorough language editing, correction of minor errors, and a careful check for stylistic consistency.

Concerning  the structure and focus, the manuscript combines experimental calibration details with the description of the simulation development, which weakens the clarity of its scientific focus. The experimental setup should be clearly presented as validation infrastructure rather than as part of the novelty of the work. In the abstract, the paper is described as a simulation study, yet a physical setup is later introduced without a clear explanation of its role.
A brief statement clarifying that the experimental setup is used solely (if this interpretation is correct) to tune and validate the simulation parameters for a single SiPM pixel would substantially improve the focus and readability of the manuscript.

The current section titled "Discussion" is unclear and does not actually summarize the work or discuss the main outcomes. It mostly lists some technical details (e.g., parameters saved in configuration files) without highlighting the significance or the implications of the study. This section should be rewritten to provide a clear summary of the results and their relevance (possibly under a new title such as "Conclusions and Outlook"). In my opinion, the authors should explicitly state what was achieved, what remains to be done, and how this work contributes to the overall goal of SiPM-based Cherenkov camera simulation.

I also encourage the authors to perform a careful, line-by-line revision of the text. The following points are illustrative examples and may not cover all issues present in the paper.

- "a comprehensive simulation its response" → "a comprehensive simulation of its response."
- "INFN Naploli scottiv@na.infn.it (still Naploli instead of Napoli in the affiliation, as mentioned in the first report).
- In figure captions, use "χ²/ndf = 7.00" (and 2.07 in Fig. 6) instead of "Chi squared per degree of freedom of …".
- "between .5 and 1.5 MHz" → "between 0.5 and 1.5 MHz." Likewise, "0.7 MHz" instead of ".7 MHz."
- Review capitalization: sometimes "ADC" appears in uppercase and other times "adc" in lowercase. The uppercase form should be used consistently. The same applies to "MPPC."
- Use a single consistent form for "overvoltage" (avoid mixing "over-voltage" and "overvoltage").
- Time units: choose one style, either "ns" or "nanoseconds," and apply it consistently (the symbol "ns" is preferable).
- Equation references alternate between "Equation" and "Eq." Please select one form and use it throughout.
- "The SiPM bias voltage, readback of integrated SiPM signals" : this phrase is unclear to me; consider rewording if necessary.
- "mantissa of the log-likelihood": is "mantissa" appropriate in this context? 
- Revise the caption of Figure 7. Suggested phrasing:
  "This figure shows the linear fit to ADC counts at each PE peak."
- Check all figure captions for consistency in capitalization, punctuation, and syntax.

Comments on the Quality of English Language

The English is generally clear and understandable. However, some sentences would benefit from careful rephrasing and consistency improvements, as indicated in the report. A moderate language revision is recommended to enhance clarity and flow.

Author Response

Comment: Concerning  the structure and focus, the manuscript combines experimental calibration details with the description of the simulation development, which weakens the clarity of its scientific focus. The experimental setup should be clearly presented as validation infrastructure rather than as part of the novelty of the work. In the abstract, the paper is described as a simulation study, yet a physical setup is later introduced without a clear explanation of its role.
A brief statement clarifying that the experimental setup is used solely (if this interpretation is correct) to tune and validate the simulation parameters for a single SiPM pixel would substantially improve the focus and readability of the manuscript.

Response:  The purpose of this work is to present a novel simulation method for SiPMs that was developed for the SiSMUV (SiPM-based Space Monitor for UV-light) project. In the abstract, I introduce the SiSMUV project and their development of the Cherenkov Camera for the PBR mission before stating the need to develop a simulation. This is to clarify that the simulation is being developed for the SiSMUV project. At the end of the abstract, I clarify that the simulation reproduces the results of the test setup in Naples.

Comment: The current section titled "Discussion" is unclear and does not actually summarize the work or discuss the main outcomes. It mostly lists some technical details (e.g., parameters saved in configuration files) without highlighting the significance or the implications of the study. This section should be rewritten to provide a clear summary of the results and their relevance (possibly under a new title such as "Conclusions and Outlook"). In my opinion, the authors should explicitly state what was achieved, what remains to be done, and how this work contributes to the overall goal of SiPM-based Cherenkov camera simulation.

Response: I moved the technical details regarding the values for SiPM pixel parameters and their storage in config files to the methods section. I use the discussion section to present the results and future work as the MDPI template suggests. I also reiterate the importance of an accurate SiPM simulation to a SiPM based Cherenkov Camera experiment.

Comment: I also encourage the authors to perform a careful, line-by-line revision of the text. The following points are illustrative examples and may not cover all issues present in the paper.

Response: I performed a line by line revision of the text and fixed the highlighted issues and more.

- "a comprehensive simulation its response" → "a comprehensive simulation of its response."

fixed

- "INFN Naploli scottiv@na.infn.it (still Naploli instead of Napoli in the affiliation, as mentioned in the first report).

fixed

- In figure captions, use "χ²/ndf = 7.00" (and 2.07 in Fig. 6) instead of "Chi squared per degree of freedom of …".

fixed

- "between .5 and 1.5 MHz" → "between 0.5 and 1.5 MHz." Likewise, "0.7 MHz" instead of ".7 MHz."

fixed

- Review capitalization: sometimes "ADC" appears in uppercase and other times "adc" in lowercase. The uppercase form should be used consistently. The same applies to "MPPC."

fixed

- Use a single consistent form for "overvoltage" (avoid mixing "over-voltage" and "overvoltage").

fixed

- Time units: choose one style, either "ns" or "nanoseconds," and apply it consistently (the symbol "ns" is preferable).

fixed

- Equation references alternate between "Equation" and "Eq." Please select one form and use it throughout.

fixed

- "The SiPM bias voltage, readback of integrated SiPM signals" : this phrase is unclear to me; consider rewording if necessary.

Changed to: The SiPM bias voltage, the digitization of integrated SiPM signals (for an integration time of 80 ns), and the external trigger (activated at the same time as the input laser) are all controlled by a prototype acquisition board.

- "mantissa of the log-likelihood": is "mantissa" appropriate in this context? 

Changed to argument of the logarithm.

- Revise the caption of Figure 7. Suggested phrasing:
  "This figure shows the linear fit to ADC counts at each PE peak."

fixed

- Check all figure captions for consistency in capitalization, punctuation, and syntax.

All figures have complete sentence captions now.

Reviewer 2 Report

Comments and Suggestions for Authors

NA

Author Response

Thank you!