Off-Axis Characterisation of the CERN T10 Beam for low Momentum Proton Measurements with a High Pressure Gas Time Projection Chamber

Round 1

Reviewer 1 Report

The article Instruments 866847 deals about the characterization of the T10 beamline at CERN to study the cross sections of low energy protons in gaseous argon. 

I consider the submitted manuscript a “preparation article” since it only contains the beam characterization while the cross section measurements will be the subject of another publication. 

Nevertheless, I consider the topic interesting since the response of neutrino detectors to low energy protons is of general interest.

 

General comments/questions:

1. Considering that the approach could be of general interest and to make therefore the paper a bit more interesting, I would suggest stressing more the used approach to achieve a low energy proton beam.
2. If the aim was to use a proton beam below 100 MeV, did the authors investigate the possibility to use a proton beam from a proton therapy center? There is one in Manchester or Birmingham if I am not mistaken. 

 

The paper is well written although a bit lengthy for my taste and considering the topic. 

 

Specific comments and questions:

1. Page 2, Introduction: Since the authors are mentioning the CP violation in the leptonic sector, they should cite the recent Nature paper about this topic. It gives the impression that there was no measurement until now but the aim for the future is to improve the existing results.
2. Page 2, line 35 to line 37: Rephrase this sentence. It sounds confusing and in fact, here the T2K results are mentioned but not cited.
3. Fig. 1: I understand that the semi-empirical model is used in GENIE , NEUT, and NuWro with different parametrisations. The curves in Fig. 1 correspond to which MC generator? One shows better agreement in the case of Argon are all show a similar discrepancy?
4. Fig. 2: In the axis labels KE is used but it is not defined. Define it in the caption or in the text. I know what it stands for but it should be defined explicitly.
5. Fig 2 (right) and page 4, around line 68: Few words about the differences between the MC generators? Especially the suppression of low KE for NEUT compared to the others.
6. Page 5, Beam Test Overview: A plot should be added showing the theoretical beam composition which is provided by CERN for T10 and T9. 
7. Page 5, line 101: “.. optimal TPC position ...” what was the criterium to define the optimal position?
8. S3 and S4: I would call it a panel and not a wall. 
9. Page 7, line 119: The DAQ synchronization was done offline. How was ensured that there was no event lost in one of the DAQs during data taking. 
10. Fig 7: Remove these figures. They are not really interesting and S1 and S2 are visible in Fig. 5
11. Fig. 9 and Fig. 12: If you want, keep the schematics but only the left side for both and merge them into one figure to  make it more compact. The right side is not adding any information. 
12. Page 10 or else: Please add a diagram showing the trigger logic
13. Page 11, sentence starting in line 186: Why you show MIPs for unmoderated and protons for moderated? Either show only two for the same particle type or even all 4 plots in 4 subfigures. 
14. Page 11, line 190: You provide the FWHM information for the unmoderated beam but also should do so for the moderated one. 
15. Page 13, line 216: barA => bara or since bara is also not so much used “bar of absolute pressure” or something similar
16. Page 13, line 217: Vessel thickness ... 80 MeV. => I think more interesting would be to know the typical energy loss of proton which is not stopped. Thus, how much the energy spectrum is shifted down. 
17. Page 13/14: Some more information about materials in the beam? Cathode, ... 
18. Fig. 14: Add a plot title to the figure indicating if S1-S3 or S2-S4 and not only in the caption.
19. Page 15, line 247: Any better explanation of why a double peak? A broadening I could easily understand but a double peak?
20. Page 15, line 257: Why only charged pions? I guess it would be pions and muons. 
21. Page 17: What is the effect on the rate of the TPC in the beam? It is explained how it shifts the energy of the protons but there should be also some protons being stopped. 
22. Table 4: Why is the background increasing with blocks first and then for 3 and 4 blocks it drops again? How is the S/N ratio evolving with the number of blocks? This looks more interesting for me. 
23. Fig. 19: Compared with Fig. 16 it is interesting that the double peak has disappeared also this is not really surprising. However, any idea from where the peak at 1.75 is coming? It is not visible in the unmoderated spectrum. 
24. Fig. 20 and related in the text: I am a bit confused. I cannot see that this is a real detection efficiency. Or why is the efficiency highest in the center? I guess is is a kind of hit distribution but not really an efficiency. Make this more clear. 
25. Fig. 24: Any explanation why 4 blocks are so different to 3? The evolution from 0, 1, 2 and 3 blocks is easy to understand but then 4 blocks is a big difference. 
26. Conclusions: As mentioned before, I would propose to stress more the possibility to create in this way a low energy proton beam for neutrino detector tests.  

Author Response

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

1) In the Introduction (line 24): the words "appearance" and "disappearance" need to be switched.

2) In figure 3, left plot: the vertical axis label "Protons" applies to only one of the three peaks shown, and it should be replaced by a more general descriptor like "Events".  Also, it would be useful if the caption identified which of the three peaks corresponds to the protons.  It is discussed much later in the paper, but the time the reader gets there the opportunity to make a clear point with this plot has passed.

3) Figure 6: It is not clear until  figure 13 that the TPC is cylindrical, and that the beam is incident on the side of the cylinder.  This plot adds to that confusion, in part be cause it's representation of the angular spread of the up-stream and down-stream sides of the cylinder as rectangles is inaccurate.  For starters, the top and bottom rectangular edges actually refer to the same line is space.  Instead of rectangles these cylinder sides should have convex (TPC US) and concave (TPC DS) vertical sides.

4) Most of the histogram axis labels are confusing. First, I don't understand why the authors are dividing out the units (e.g. "/ns") instead of just reporting them (e.g. "[ns]").  In some cases, although not all, they attempt to use good form by adding the per x-axis unit to the vertical axis label (e.g. "/ns"), but unfortunately this is technically inaccurate when they have canceled the units on the x-axis.  If they wish to cancel the x-axis units then the correct thing to do with the y-axis label is "/bin" or "/4 bins", but I do not recommend this approach.  Of course all histograms should have appropriate per x-axis units, and most do not.

Author Response

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

General comment: since the paper uses many place the particle’s momentum of 0.8 GeV/c, though it can be found in the reference on the PS, but it’s better to state how this particular momentum is selected.

Specific comment and question:

Figure2: add period to the end of the caption; add title to the Y axis; ideentification -> identification.

Figure3: add period at the end.

Figure6: legend drawing option “LP”, remove the “P” option since only the lines are shown

Table1: the maximum theta value for S2 is -0.36, however, reading from Figure6, the maximum theta for S2 is positive, please solve the discrepancy.

Table1: for S4, please correct the “degree” symbol for maximum theta and minimal phi to make them the upper case in consistency with others. 

Figure7: add period at the end of the caption.

Line 150-151, it’s better to indicate the light guide for S2 in either Figure 5 or Figure 7, this might not be so straightforward for non-expert to understand.

Figure10: period at the end of the sentence.

Line 202, add comma between “give position” and “Figure 11”

Figure 11, the fit fails given the large x2/ndf value, and the binning is too coarse. Can you show the histogram with a finner binning?

Line 200, can you explain the difference in the measured time resolution between S4 and S3? 800 ps vs 100 ps is quite big difference. Qualitative explanation should work here.

Figure 21, please show the quality of the fit in terms of x2 and ndf. In the plot, it’s advised to add the signal and background functions from the fit independently since you’d like to state the background function is flat.

Figure 22, right: please indicate how to select the protons crossing into the TPC, e.g. do you require hits in the readout wires? If so, please give a detailed description on the selection cuts in the text.

Figure 22, add a period at the end of the caption.

Lines 330, 338, 340 and legends in Figure 22 right, Figure 23 and Figure 25, please explain how are the errors calculated.

Figure 24, remove the period before the last “and”.

Line 412 and 414, Sr90 should be consistent with 90Sr at lines 200 and 202.

 

Author Response

 

 

Author Response File: Author Response.pdf