sPHENIX EMCal discussion

[EdwardOBrien <eobrien AT bnl.gov>]

    Dear all,
     I've done a complete read-through of the draft of the sPHENIX
    pCDR and have been impressed by the quality of the text and
    the level of level of detail in the document so far.

    I have many comments for the authors and contributors to consider.

    Ed



    We need to add a chapter of Detector Overview and Requirements
    immediately after the Scientific Objectives chapter. The Overview
     chapter needs to contain much of the information in chapter 2
    of the sPHENIX Proposal.

    Complete the missing sections on the Si strips for the Tracker and
    the Project Management chapter.

    The magnet chapter needs more discussion of the magnet acceptance tests
    including both the warm test, low power cold test and the full field
    test.

    Both the cryo system based on tapping into the RHIC cryo and a stand
    alone cryo system should be discussed. Currently only the stand alone
    system is mentioned in the text.

    A description of the magnet flux return should be included in the 
Magnet chapter
    in addition to the results of initial magnetic force and field 
calculations.

     In general the design of sPHENIX components should be referred to
    as the "reference design". We're a couple of years from having a final
    design.

    The EMCal chapter was repetitive in its description of tower design and
     tower production issues. Please clean that up.

    The HCal chapter contains 14 pages describing the R&D and test beam 
effort.
    This is far too much. The emphasis in the R&D section should be on 
what we
    have learned so far and what still needs to be answered in future 
bench and beam
    tests. Remember that the pCDR is not a status report.

     The Installation section 9.3 contained too many bulleted lists. Where
    appropriate convert them to paragraphs.

    Many figures are still needed.

     Other comments:
    Figure 1.23. What does the color band at the top of the figure mean?
    Magnet 2.1.1. Mention when the magnet was produced (1996?). When it 
arrived at BNL
    (early 2015)
    Figure 2.6. This figure may be too faint for the document.
    Section 2.2.7 Cryogenic plant. Describe both the stand alone option 
and the tapping into
    RHIC cryo option.
    Secton 2.3.3 In the Energy Extraction subsection we need a 
statement that the set-up
    with the dump resistor poses no risk to the equipment, or safety 
issue during a quench.
    We should state that the quench effects had been analyzed and that 
there was
    no equipment hazard.
    Section 3.4 TPC electronics It would be better to call for 100k 
channels/side rather than
    90k, because that implies a more accurate knowledge of the channel 
count than we currently have.

    Section 3.4 quotes the sPHENIX interaction rate ~ 25 kHz, I believe 
that this is the max rate inside
    +/- 10 cm, not the MB rate inside the full diamond.
    This section contains too many undefined acronyms, LTU, FEC, GBT to 
name a few. Please fix.

    EMCal chapter 4. Use electron-hadron rather than electron-pion 
where appropriate.
    Secton 4.2.2 A figure here showing the different modularity of the 
detector would help,
    tower, module and sector.
    The stainless steel box is "thin-walled", not "thin"
    The description of the tower fabrication which starts," Making the 
fiber taper in 2 dimensions..."
    is too detailed .
    Instead of "we are working to improve the quality of the ends...", 
write," The quality of the
    ends of the surfaces are very improtant to the performance...."
    Section 4.2.3 Discuss both the THP and University assembly options 
as two equal possibilities. I
    think that they are equally likely. Replace "We hope" with "We expect".
    Section 4.3.2 "Energy resolution for electron showers is reproduced 
within 10% relativity"
    What is "relativity"
    Sections 4.3.3 - 4.3.7. Should they be moved up in chapter 4 to be 
near the beginning of 4.2?
    Section 4.5 Alternate Technologies. Make a stronger argument 
against the 2 options
     listed. As currently written they don't sound bad to me. For the 
reuse of the Babar
    CsI mention that for a 1 usec decay time and a RHIC AA 100 kHz 
collision rate that means
    10% of the events have two HI collisions. At the same time the CsI 
Moliere raduis of 3.8 cm
    rather than 2.2 we will have 3x the occupancy.
    Also is PbO4W really $5/cc produced vs $1.5/cc raw material for the 
W spacal? If so then
    for a reasonable labor cost for the spacal production I would 
compare $5/cc for PbO4W
    vs $3/cc for a produced spacal. Perhaps not as strong an argument. 
Isn't the number
    really $10/cc for PbO4W and $2.5/cc for the spacal?

    Section 5.3 HCal. In the paragraph that starts "The basic 
calorimeter concept..."
    call the calorimeter design that we've chosen a "tilted-plate 
calorimeter". State
    the tilt angles in the reference design, 32 deg for the Inner and 
12 deg for the Outer.
    State that they are projective.

    Section 5.3.3 Outer HCal. The text should be more descriptive.
    Section 5.3.4 should be titled "photosensor and readout 
electronics" Add more detail
    LED calibration: Eric showed a figure at the EMCal review
    Figure 5.3-5.7. The figures need better captions. Which are Inner 
and which are Outer?
    Get crisper figures. Some are fuzzy.
    Figure 5.11 fix the labels and combine with figure 5.15.
    Section 5.5 is too long. Reduce to 5 pages.  Far too much detail on 
the test beam work.
    Write was was learned and what tests remain to be done both on the 
bench and
    in the test beam. Remember that this is not a status report. It is 
a design document.

    The HCal section needs a description of the mechanical analysis 
performed and its results.
    Write more for section 5.6 alternate designs.

    Chapter 6 Calorimeter Electronics:  1 paragraph "... shaped and 
differentially driven to
    to digitizer boards located near the detector.." change to ".. 
located in racks near the
    detector.."

    Figure 6.2 add dimension of the component in the caption. You can't 
tell how
    big it is from the picture.

    Section 6.1.2 Neutron radiation Effects: This section states what 
was done, but it needs to
    also state the conclusions from our tests. Neutrons in the MeV 
range are the dominant
    contributor to the damage. Thermal neutrons have little 
contribution. The total expected
    neutron fluence for two years of RHIC running is what? Where is the 
reference to figure 6.11?
    6.2.3 Where is the slow controls and monitoring located? In the 
racks? Is SEU an issue?

    Section 6.2.4 " "The reference design digitizer electronics for 
sPHENIX is based on the
    digitizer system built for the PHENIX HBD and modified for the 
PHENIX RPC". I think
    that this should be "...modified for the PHENIX MPC.." Isn't that 
correct?

    Figure 6.11 is very important. The text should emphasize why this 
plot matters. The rad
    damage to the SiPM doesn't change the pedestal in a significant 
way, only the bias
     current draw.

    Chapter 7 DAQ/Trigger: Paragraph 5 "..to achieve the envisioned 
rate.." should be
    "..to achieve the expected rate.."
    The section numbering needs fixing in chapter 7.
     Section 7.0.9 Triggering Do we need to add a discussion of the 
GL1. What about
    the need for a LL1 board for an EMCal energy trigger?

    Section 8.4 Beam pipe. Update and correct. State that no 
modification to the Be section of the
    existing beam pipe will be necessary.
    Section 8.5 Shield wall. State that sPHENIX can fit through the 
existing opening in the
    current shield wall with no modification.
    Figure 9.2 Do we need to have a figure just showing the sPHENIX 
coordinates?
    Perhaps it should be added to another figure.
     Chapter 9 contains a lot of bulleted lists. Some lists should be 
written as paragraphs
    where appropriate.