CDC NIM Elton

-- Answer from authors

-- Change applied or not applicable due to previous changes

General comments

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Introduction needs to review in more detail general GlueX experimental conditions. Many of these are aluded to througout the document, but it would be useful to have a good summary at the beginning, including:

1. Type and energy of beam

2. Expected rates in detector

3. Multipliticity of physics events. Goal of detection of charged and neutrals. Should give Ref [11] in the intro (perhaps even reference Bcal NIM paper), and not wait till Summary. Found inspiration in the BCAL paper

4. Minimum and Maximum distance of detector from beam. I do not see that this is given anywhere. It is encoded in the introduction

5. Note that full tracking will be achieved using both CDC (central region) and FDC (forward region).

6. Configuration of planes could use a picture of a phi slice listing the stero/axial regions.

7. Description of end-plates and plenums. When the electronics is discussed in section VI this information is needed as background. One could wait till then to discuss it, but I think it makes more sense to cover it in the introduction. E.g. where the electronis is located (upstream), how the gas will flow through the detector (upstream though straws to downstream plenum) and exhausted. All cabling will be done upstream. etc. -- Need to include motivation of radiation studies and what can be/has been learned from electron microscope photos. For example, since we will be in a low-radiation environment, why is this a concern, or what are we looking for? I must say, that it is hard for me (unexpert) to discern what one should look for in Figs 6-10. Text would be useful to guide focus and interest.

References: Would be useful to cite other straw-tube designs. How is this chamber different/similar? What tests are done here that are not available in the existing literature? What gas choices were used in other chambers? What resolutions are achieved in other chambers? What are the challenges of using dE/dx in a straw chamber? (It has been used extentively in other wire chambers).

Nobody else makes a comparison with other straw chambers, also there is a lot to compare to.

General comment on tense: Suggest changing tense. Historically, scientific documents are written in the passive tense "...details will be provided in..." but a more recent convention (for clarity) is active "We provide details in..." I'm no expert, but it is worth having someone with good writting skills (likely not a physicist) comment on language. [We have resources at JLab that could do this for a final draft if desired]. I will not edit to this detail at this point. We probably need to do that in the end. I tried to change it where-ever people or I saw it.

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Specifics: (line number:) 17-18: Material along tracks is not minimized, except in the region of the endplate. This is covered in the last paragraph sentence. I suggest eliminating this sentence, and change "One advantage..." ->"The advantage..."

23: resolution aimed for... -> goal for resolution transverse to the wire is 150 microns and 1.5 mm along the beam direction [or axis of the chamber].

41: Is 1.6 cm the inner or outer radius (specify)

41: Move 47:Fig. 2... to follow first line of paragraph

Suggestion in this section: Do we want to suggest that the design of donut/feed thus/etc was designed to make a good gas seal and... has been successful? Refering to other chambers, this could be identified as an improvement in the mechanical design.

Fig 4. Looking carefully at the picture it appears to have seveval glue lines. (Am I correct? If not, the picture is not very useful, or even deceiving). If so, instead of having an one oval (implying a single glue line), indicate all glue lines with arrows and mention the number of glue lines in caption.

57: It is worth motivating the sagging and radiation in the sentence that introduces the tests.

60: For all vendor identification, it is common to use footnotes with specific contact information. For example 'CA fine wire' should (I think) be California Fine Wire \footnote{California Fine Wire, address and web link if available}. If the wire can be identified more specifically also do this.

General comment: One use of NIM articles is to trace materials to sources and we should try to provide sufficient information for anyone to do this by using this article.

64: I suggest changing this section into "Straw -> Mechanical sag. (Distortions due to gravity?) Is it worth mentioning the sag of the wire?

65: aluminised -> zed for American 65: Lamina. Company reference, see note for 60: 67: Missing period

68-69: Statement about gluing should be removed since paragraph 72-80 motivates and repeats this sentence.

69:71 I would remove this sentence and make the the section on sagging only (see note on 64:)

81: I think it is worth motivating the radiation testing, since we do not expect high rates in the detector. Also, in addition to electron microscope photographs, I thought you checked the gains before/after irradiation. This would be more quantitative. Did the gains change/ or any other parameter change?

General comment for the 300 Angstron thickness. I would suggest to quote the thickness of the Al layer for all straws in microns [300 Anstrons-> 0.03 microns] for consistency. This makes the comparisons between different straws more transparent.

Additional note: for the Sprial Paper Tube, the "unknown thickness" could use a footnote stating something like. "The thickness is likely to be between ... and ... based on ....." Or has a thickness similar to the .... straw. 102: Was the source really a 1 Ci source? No, it was a 100 muC, good catch

Figs 6-10. The scales are invisible on the figures.

Section C General: I suggest to use "unused reference" instead of "straw that was not used"

110-113: Suggested wording: "During irradiation the prototype flowed an Ar-CO2 (90%-10%) gas mixture and set the wire at the nominal operating voltage of 1450 V. The straws were grounded. Irradiated straws were later compared to unused virgin (reference) straws that were neither irradiated nor used in a chamber with gas or HV.

[Note: I assume "slightly above atmosphere is due to the bubbler." I would ignore this difference as the comment actually implies a pressurized chamber.]

115: in [2] -> in Ref. [2].

117: -> A piece of an unused reference Lamina-thick straw was compared to an irradiated piece using electron microscope photos.

143-148: Statement should be re-evaluated based on new information about thin and thick Lamina samples.

150: wire was also examined (omit being) 152: for different scales... Which scales? at 10 microns? 153: Should give an estimate of the accumulated charge expected for GlueX. 44 years or more

157: Section D. In the introduction (or perhaps here), I suggest a figure showing the axial/stereo layer structure of the chamber. Could also indicate min/max distances from the beamline.

166: Rearrange: ...of two MKS Instruments Inc. \footnote{See 60:} mass-flow controllers (one for argon and one for CO2 gas). [Note If Mass-Flo is a brand or controller type it can be capitalized and spelled this way.]

169: Suggestion: The design includes the option to ...add a hydrocarbon gas but for safety reasons it has been avoided. [No need for Jeff lab reference]

174: gas flow (in the prototype?) is a few detector volumes per hour. We anticipate about three volume exchanges per day for the gas system in the GlueX detector.

IV. Electronics

Need to describe location of electronics (readout electronics, location of HV, input and output gas, cabling....etc). I suggest this be done in the introduction.

Fig. 11: Suggest the use of the name "full-length" prototype. For the figure specifically one could label it "one quarter section of a full-length prototype of the CDC."

183: First mention of "end plennum". Needs previous reference/description.

189: Suggestion: The charge-amplified signal of (the current prototype(s) is/are) shaped by a shaper board [7] and readout by a Struck SIS3320 \footnote{ see 60:} Flash ADC running with a 125 MHz external clock. In the GlueX experiment, ....

197: full scale -> full-length

206: Suggestion if I understand the test correctly: Tests were also done to compare the options of placing the electronics either inside or outside the gas plenum. Both configurations could be implemented in the experiment with acceptable distance between the wire and the preamplifier(?) so we chose to locate the electronics outside the gas plenum to facilitate access.

217: ...were corrected (when building a) small prototype

Fig. 12: left-> top, right_> bottom

232: MC simulation (was adjusted to measurements?), and gas...

Fig 13: Suggest changing colors of active black-> red, and dead red->black. Also, I think this figure could be quite useful in discussion of fitting CR tracks (VII.C.2) if a track is indicated with drift radii, etc. It could also substitute for Fig. 22.

233, especially 242: Section A Would be useful to parameterize the resolution as a function of gas mixture. That would provide a quantitative output to this study.

244: Section B. If I read this section, the first question that comes to mind is why is the angle computed with the energy and not the drift times. If I understand the motivation, it actually has to do with the dE/dx resolution. But this motivation is not mentioned and the entire discussion of dE/dx is in VIII. As far as I can tell, there is nothing needed from this section prior to VIII, so I suggest to move the entire section VIII as an experimental test of the measured energy-loss distributions. I will proceed to make comments to this section, but assume it could be moved back to the later section.

Need a section to motivate the study of response to different angles. For example: The fixed-target configuration of GlueX results in most of the tracks crossing the CDC at shallow angles. As the energy loss in each straw will be inversely proportinal to cos(theta), where theta is the scattering angle, the energy loss measurements need to be normalized to mantain sensitivity to particle identification through dE/dx. Experimentally, the sensitivity can be demonstrated by using the measured energy loss in the chamber to compute the angle of incidence...

I added more motivation, the motivation is not what you described. It is more like a mechanical test. If the detector does not behave as expected - deviations will be observed

Now start with Eq. (1): Presumably the reconstructed angle (displayed in Fig 15) has the sensitivity because it is an average over a sample of hits in a given wire. One should specify what the statistics is. For relevance to the dE/dx measurements, it would make sense to take this number equal to the number of layers (28). That way the average obtained is essentially equivalent to a measurement along one of the tracks, assuming that there is no systematics in the respoonse (or they are adjusted) between wires. 28 hits is not sensitive enough to make such a nice reconstruction

For Fig. 15: I suggest to plot not only the mean (as indicated), but also the width determined by the width of an individual measuremente (Fig 14), divided by the number of measurements, e.g. sqrt(28). Error on the mean will not be visible

262-266: If I understand correclty, I think the 0.92 "is the solid angle correction to the trigger counters, which systematically moves the average track angle with the chamber is in its horizontal position." 275: Those random points (generated according to the cosmic-ray distribution ? -- or assuming a flat cosmic ray distribution?) Flat 279-280: Those (pulses) are convoluted... 282: obtained (empirically) by injecting... 290: ...this method is that it can include the effects of the magnetic field on the drift chamber response using GARFIELD but still work with straight tracks.

298: and fit to the measured spectra with the gas gain as the single (unknown) parameter.

Table II: Also for other tables. First line: Put [%Ar-%CO2] on the second line of the title. Make all the columns be |c| to center them. For the last column (gain) add units on the second line of 10^5, so that the entries are 1.5 .... etc.

321: normalizeD

Table III (see comments on Table II)

335: B. Drift times (for B=0)

One distintive feature of this detector is that the readout is using Flash ADCs and no TDCs are used. Therefore, the timing must be obtained from sampling the pulse. It might be useful to add and introductory sentence or two to start the discussion.

340: rising edge relative to what? trigger counters? 343-349: I do not understand the method described here to extract the drift time.

Eq. (2): Is this algorithm practical with FADC micro-code. Is it necessary? Can be simplified: the price is 8 micrometer in resolution

Fig. 18: Labels too small for article. Add % mixtures of Ar-CO2 on plots if possible. 368: Missing period. Add: for the case of B=0. See section C.4 for a discussion for the response in the magnetic field environment of the experiment.

Table IV caption: Table containing the maximum drift times for... What about combining Table IV and V by adding a third colum for B=2.24 T. That will make it easy to compare and also immediately address the reader's question about the relevance of the table to the actual experiment.

369: C. Resolutions. I made this comment ealier, but it would be quite useful to work on Fig. 13 to illustrate tracking in this section and the determination of resolutions.

The "distance of closest approach" DOCA (in CLAS jargon) seems to be called the drift radii(375:) / hit-radius (384:)? It is somewhat unclear and must be quantitative for this section. (I am especially confused by Eq. 3 below). Again, a figure is worth a thousand words.... Fig. 13? 386: combination - how may and which ones? All of them 387: members? of the track. Is this the same as hits on the track? 390: Suggestion: ...best residuals if the candidates have the same (number of hits) is kept as (the) found track

Eq. (3):

1. I do not understand how this can be true unless x and y are measured relative to the wire positions. Also why is the function normalized by A^2+B^2, unless dimensions are normalized to the straw radius?

2. Denominator: the energy of the hit is not used, just eliminate from equation as it causes confusion (or use sigma_hit^2, assumed to be constant, and state that optionally sigma_hit^2 could be set to the energy depostion on the wire).

416: Suggestion: description of the data, givign confidence that the MC can be trusted to extrapoate to the case of non-zero magnetic field. 419: To examine the resolution... 421: The (simulated resolutions are shown) for different... 424: ...the resolution goal of 150 microns can be obtained for drift distances longer than 1mm if the CO2 content is greather than 40%. 427-431: Move this statement back to the section of B=0 #3 and connect with Fig. 19. It can be re-emphized here if desired, but presently it appears this is an effect caused by the magnetic field. Fig 19. Remove red line. Add single note at end of caption: The resolution goal for the chambers is 150 microns. I like the red line 432-437 (including Table if not combined with Table IV. Move to beginning of section, because the improved resolution is really just a result of the long drift times, so it naturally should be discussed second (as it is for the B=0 case). 435: Suggestion: All gas mixtures satisfy our requirement that tmax<1micros, although the 40-60 mixture comes close to that limit.

438: Reword: The gas mixtures.... satisfy all the requirements....

440: Reword: An added advantage to these mixtures is that no flamable components are needed, which minimizes safety concerns.

450: Add sentence at end: However, our close-pack design will ensure high efficiency for hits in adjacent layers.

451: VIII. Consider moving VI.B 'tilted' chamber to this section.

452: Suggestion: In order to determine the effectiveness of this chamber to identify pions, kaons and protons using energy loss (dE/dx), we undertook a Monte Carlo study based on the realistic simulation described previously. Move (modified) sentence 461: up to here There is no intention to give a complete description of particle identification here, but rather to investigate the principle. Now continue with paragraph starting in 454: "Pions, kaons and protons, were generated....

Fig. 22 Could use Fig 13 to illustrate this effect as well as other aspects of track segment finding.

General comment/suggestion: I would drop Section B (250 MeV Pions and Kaons) and spend more time to discuss how to move from Fig. 23 to Fig. 24. As it is, Fig 24 is so small it is quite difficult to read labels and the two plots will likely have to made larger. Qualitatively Fig 23 and 25. are quite similar and in a sentence or two one can describe the increased sensitivity between pions and kaons at lower momenta.

465: In Fig. 23 the (simulated) dE/dx... 466: ...are shown. (The) expected.... 469: several layers combined. [How many?] 472: Reword (and omit repetition in 483 if section remains): We note that optimal use of the energy loss information would be to include it into a kinematic fit which incorporates all relevant information available in the event.

486: ...the (full-length) prototype... 493: the (position along the wire) direclty. This charge division can thereby provide complementary information to that obtained from a combined analysis of stereo and axial wires. 501: the (GlueX experiment, mostof the) signals... 503: resolution (along the wire) of about 10 cm. 504: ...can be found in (Ref.) [12].

508: detail. (Many) design choices 509: etc.) have been determined by comparing experimental data from prototype chambers with MC simulation. 513: Refer to Ref. [11] in the introduction

General bulleted suggestions for last half of conclusion:

Features of this chamber:

• straw tubes with potential to perform particle identification using

energy loss measurements (common in other types of chambers).

• extraction of timing information using Flash ADCs.

results:

• Detailed measurements of components for chamber have been performed
• Developed realistic MC that reproduces experimental results. The

simulation has been used to predicte the expected particle identification sensitivity using dE/dx.

• Test of charge division by connecting neighboring wires has been

conducted that shows that position resolution of about 10 cm can be achieved along the direction of the wire.

References: General: need to expand reference list to point to other relevant chamber studies to compare and contrast with this one.