[Halld-pid-upgrade] GlueX DIRC internal review
Curtis A. Meyer
cmeyer at cmu.edu
Tue Sep 8 21:53:44 EDT 2015
I don’t think that the suggestions are 100% compatible suggestions, but my take is the following:
1) in the introduction, add a bit more physics justification for the DIRC.
2) Discuss the limit of the current PID systems and at least have material
on why we cannot do a “cheap” TOF upgrade to accomplish the same
results.
We have a really nice plot of PID in the TOF now, and we are
basically at design specs. It is pretty obvious that kaons die off by
2 GeV/c and I doubt that anyone would argue that we could push this
to 4.5 GeV/c so Mike’s comment on a paragraph, with the figure,
probably covers this.
3) Some rearrangement of the existing material to smooth out flow. I
don’t have a strong opinion on this.
Probably also worth noting is that Jerry will probably be one of the
most careful reviewers who questions a lot, but also very supportive.
He wants to see the DIRC continue to do good physics.
Curtis
---------
Curtis A. Meyer MCS Associate Dean for Faculty and Graduate Affairs
Wean: (412) 268-2745 Professor of Physics
Doherty: (412) 268-3090 Carnegie Mellon University
Fax: (412) 681-0648 Pittsburgh, PA 15213
curtis.meyer at cmu.edu http://www.curtismeyer.com/
> On Sep 8, 2015, at 9:18 PM, Michael Williams <mwill at mit.edu> wrote:
>
> Today was registration day at MIT, and we had a "welcome" for the new grad students so I didn't have time go thru them all in detail yet.
>
>> Thanks for forwarding all the reviewer comments on the TDR. I felt that a number of
>> the broader issues such as physics impact and expected/current baseline PID
>> performance would be addressed in the first presentation at the review. However,
>> we may want to revisit including some more of this in the TDR.
>
> I think for the TOF, we can just add a single paragraph on this. For the other stuff, I'll need to look at it a bit more.
>
>> Do we want to wait until Friday to discuss our response? I suspect that the simple
>> things can just be fixed, but there are a couple of bigger changes that we should
>> probably discuss (perhaps by email)
>
> If somebody (Justin?) wants to go thru and just fix minor typos, etc, that's fine with me. I'm also OK with discussing the bigger things via email in advance of Friday's meeting. It would probably help if we each at least sent some thoughts on it, so that we've each thought about it properly prior to Friday's meeting.
>
> M
>
>>
>> Curtis
>> -------
>> Prof. Curtis A. Meyer
>> Department of Physics
>> Phone: (412) 268-2745
>> Carnegie Mellon University
>> Fax: (412) 681-0648
>> Pittsburgh, PA 15213
>> curtis.meyer at cmu.edu <mailto:curtis.meyer at cmu.edu> http://www.curtismeyer.com/ <http://www.curtismeyer.com/>
>>
>>
>>
>>
>>
>>> On Sep 8, 2015, at 1:19 PM, Justin Stevens <jrsteven at mit.edu <mailto:jrsteven at mit.edu>> wrote:
>>>
>>> Hi All,
>>>
>>> Attached are Dave's comments on the TDR.
>>>
>>> -Justin
>>>
>>>
>>> On Sep 8, 2015, at 11:21 AM, Justin Stevens wrote:
>>>
>>> > Hi All,
>>> >
>>> > Below are comments on the TDR from Joe and Carsten. Please take a look at these and contact them if you have any questions about their comments. We'll discuss these more on Friday. We should have the remaining comments from Dave Mack later today.
>>> >
>>> > Thanks to Joe and Carsten for taking the time to review the TDR!
>>> > Justin
>>> >
>>> > Begin forwarded message:
>>> >
>>> >> From: Jochen Schwiening <J.Schwiening at gsi.de <mailto:J.Schwiening at gsi.de>>
>>> >> Subject: Re: GlueX DIRC internal review
>>> >> Date: September 8, 2015 7:39:14 AM EDT
>>> >> To: Justin Stevens <jrsteven at jlab.org <mailto:jrsteven at jlab.org>>
>>> >> Cc: Carsten Schwarz <c.schwarz at gsi.de <mailto:c.schwarz at gsi.de>>
>>> >>
>>> >> Dear Justin,
>>> >>
>>> >> Carsten and I read the TDR draft and would like to congratulate you and the other authors on a well-written manuscript that, we think, is very close to ready for the DOE review. The text reads well, seems to be complete and the case for the DIRC upgrade is quite convincing to us.
>>> >>
>>> >> We have have a couple of suggestions and comments for your consideration to perhaps further improve the draft.
>>> >>
>>> >> We would like to suggest that you add a subsection at the start of the TDR (perhaps in section II Requirements) to motivate the 3 s.d. pi/K separation coverage to 4 GeV/c explicitly.
>>> >> My experience is that any reviewer is grateful if you summarize the main argument in favor of spending a significant amount of money on a new system right up front instead of pointing to the PAC information in the references. A couple of benchmark channels that highlight the additional physics reach would be very helpful. I think that this is the plan for the review presentation agenda anyway, so this seems a natural and useful addition. A nice eye candy figure would help sell the FDIRC idea.
>>> >>
>>> >> The central point of the TDR is the design of the expansion volume since it is the main new development. This could be emphasized by changing the sequence, for instance, to
>>> >>
>>> >> Introduction
>>> >> FDIRC Design
>>> >> Focusing Box Design <---
>>> >> Photon Detection and Readout
>>> >> Integration and Installation
>>> >> Prototype Program
>>> >>
>>> >> We missed a technical drawing of the focusing box with dimensions and angles in the first part of the TDR. We feel that a larger version of Fig. 41 should appear somewhere around page 10 (in that new "Focusing Box Design section) and that the baseline design of the focusing box should be described in detail there.
>>> >>
>>> >> We would propose to move the discussion of the tracking resolution (last para in II, Fig 2) to a section where the expected/required DIRC resolution is discussed in one place. The draft would profit from an explicit discussion of the expected Cherenkov angle resolution for these BaBar DIRC bar boxes. A breakdown of the correlated and the single photon resolution terms with the contributions from the bar imperfections, chromatic dispersion, pixel size, and focusing uncertainties (incl. kaleidoscopic effects) would help to motivate the mirror design and should precede the estimate of the correlated terms. Jerry will want to see this breakdown to understand which effects dominate and how much effort, for instance, needs to be put into the mirror design/alignment.
>>> >>
>>> >> We propose to rephrase the design description in terms of "baseline design" and "design options" to make room for possible improvements to the design as a result of the ongoing simulation work.
>>> >> Mention either the single focusing box or the two focusing boxes as baseline design, the other one and the 4 box solution as options that are being studied with the goal of cost/performance optimization.
>>> >> This also goes for the mirror layout, where the various offsets and angles could be described as options.
>>> >> This structure would help to keep a clear line of arguments in the TDR without too much clutter from technical details.
>>> >>
>>> >> The performance example in Fig 11 should be shown for a relevant momentum, 3.5 or 4 GeV/c, not 5 GeV/c, if possible. This figure is sort of a figure of merit for the design and looks less than impressive due to the unfortunate choice of momentum.
>>> >>
>>> >> We are missing a discussion of the plans for measurements with the prototype, if any. Do you plan to verify the design with a single-box prototype in test beams or cosmic rays? Which optical tests are planned, which resolutions or photon yields can you measure? Where can you profit from prototype tests for CLAS12 RICH, to demonstrate the photon yield and timing properties of the sensor and readout chain?
>>> >>
>>> >> Some other minor comments:
>>> >>
>>> >> General: we would prefer GeV/c as unit for momentum instead of GeV
>>> >> Fig 1: is there a version of the drawing with the DIRC in place?
>>> >> Fig 3: it would be useful to show Fig 20 from the BaBar DIRC NIM paper (Schematics of a DIRC radiator bar in side and top view.) here as well to establish the make-up of a bar, define the dimensions and angles.
>>> >> Page 6: the nitrogen flow is not really to preserve angles but to prevent surface pollution and photon loss.
>>> >> Fig 4: it is more customary to use momentum as unit for a and b, c is missing the axis label and the information on the number of particles used and the caption for b is not correct.
>>> >> Page 7: the focusing is not really directly related to the ability to mitigate the effects of chromatic dispersion in an FDIRC, that is more of a fast timing issue.
>>> >> Page 8, Fig 9: "local arrival time" is an unfamiliar term for me, maybe "photon time of propagation (TOP)" would be clearer?
>>> >> Page 10: do you mean the photon detection efficiency instead of quantum efficiency? I assume you apply a weight based on the combined QE, collection efficiency, geometric efficiency/packing fraction, etc?
>>> >> Page 11, Fig 10: The kaleidoscopic effect is not very visible in this figure.
>>> >> I think we have nicer examples from Roman's G4 sim now and/or maybe a zoom insert would be helpful and a brief explanation of the effect. Jerry is always very interested in a proper discussion of this aspect.
>>> >> Page 12: the BaBar DIRC geometric reco method does not store Cherenkov angles but the photon propagation vector "kBar" in the look-up tables.
>>> >> You could refer to the time-based imaging methods here that are being studied for the Belle II TOP and the PANDA Barrel DIRC.
>>> >> Fig 11: please explain the term "ROC".
>>> >> Figs 14, 16, 17, 19 are very (too) small.
>>> >> Page 13, Fig 15: how is the PMT are defined? Do you require a certain percentage of photons to be detected for each radius value?
>>> >> Page 13, 14: A focusing mirror is usually better than the approximation via a segment mirror. The reason why the three-segment mirror performs
>>> >> better for some angles should be discussed in the text.
>>> >> Page 14, Fig 18: we were a little confused by the use of the word "dispersion" when it comes to the mirror resolution. Do you mean image distortion or imaging errors?
>>> >> Page 16: mention that the difference between measured and expected photon propagation time can be used to reject EM background photons (as was done in BaBar).
>>> >> Fig 21: can you simply rotate the figure to agree with new bar box orientation?
>>> >> Page 19: did you consider PHOTONIS Planacon MCP-PMTs? Those are definitely ready for use and have many attractive features (but a high unit cost). Jerry will probably ask why not if you don't mention it here.
>>> >> To me the main improvement between H8500 and H12700 is not so much the QE but the clearer separation of the single p.e. peak from the pedestal. At least one should mention that.
>>> >> Fig 23 and 31 are not mentioned in the text, please add the reference.
>>> >> Page 21: do you really mean an occupancy of 0.7% per MaPMT, not per pixel?
>>> >> Page 24: add "Mechanical Design, ..." to the title?
>>> >> Page 25: It would be nice to add a few words and a drawing about the mechanical design and support of the photon camera/focusing box here. More detail would be useful.
>>> >> Fig 38: from the text it is not clear to me what significance the color of the round image blob has and if the diameter of the blob is a function of the imaging properties or of the setup (mirror radius and distances).
>>> >> Fig 39: do you want to comment on the poor signal to background ratio obtained for the 345nm LED compared to the blue LED? Also, I am not a fan of a zero-suppressed y axis, which hides such problems.
>>> >> Page 31: the discussion of the box design, as far as it concerns the GlueX design and not the prototype design, should come earlier.
>>> >> Page 32: I think the box will be mounted vertically, no?
>>> >> Page 35: do you really want to supply continuous N2 flow? It seems unnecessarily complicated, a double-bag with N2 fill should be sufficient, no?
>>> >> We agree that additional drawings and photos should be added since the transport of the precious bar boxes will be a major concern for DOE and for Jerry.
>>> >>
>>> >> Please don't hesitate to contact us if you have any questions about our comments.
>>> >>
>>> >> Best regards,
>>> >>
>>> >> Carsten and Joe
>>> >
>>> >
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