Oct 27, 2008 Calorimetry

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Items for followup from Oct 13 meeting

  1. Each subsystem must complete blanks in the Calibration Specification Table.
  2. Tests of Fcal magnetic shields (Tim and student).
  3. Decision on Bcal sampling fraction needed if any changes are to be made to design.
  4. Resolution studies (Blake)
    • Develop criteria for evaluating resolution studies
    • Up-to-date geometry ONGOING.
    • Decreased threshold for FM pmts. ONGOING
    • Position resolution - understand dependence on granularity.
    • Different segmentation for the outer section. - LOWER PRIORITY
  5. Study impact of inactive material at the end of Bcal on acceptance.
  6. Add F100 rad hard glass to simulation. - New graduate student has been assigned this project.
  7. Add roadmap for Bcal Roadmap to wiki (Elton)

Items for followup from Oct 27 meeting

  1. Check what configuration (thresholds, step sizes, stack? parameters for secondaries, etc) is being used for the Hall D simulations (Regina)
  2. Updated schedule with new Fcal procurement dates. (Elke will send this to Matt)
  3. Report on the Bfield components in the region of the Bcal reaout (JLab for next meeting).
  4. Updated drawings of Bcal modules (including O-ring) for discussions. Tim will see if that can be fitted into designer tasks.

Documents to Review

(W. Brooks) Some time ago I promised to provide a study performed by Etienne Burtin in 1995 of the CLAS forward calorimeter performance, particularly, the sensitivity of the sampling fraction to the GEANT cutoff. It turned out that there was no software copy known to be available, but a hardware copy resided in the author's office; he kindly photocopied it, and hand-carried it to CERN for me, and I scanned it in. Figure 3.7b is the plot of interest, in scanned page 10 or the document's page 59.

It's too big to download into the wiki, so I linked it from here:

http://www.jlab.org/~brooksw/burtin_thesis.pdf (~6 Mbytes)

Tentative Agenda

  1. Announcements
  2. Calibration
  3. Fcal
  4. Bcal
    • Decision on use of Getter#1 and no Getter units in the construction of arrays. Discussion
    • Decision on lead thickness
      • Updates on sampling studies (Stamatis) Media:Meeting271008.pdf
      • Comments by Will Brooks on Hall B thesis (see above).
      • What is the gain? What needs to be tested if a change is desired?
    • Roadmap toward a decision for the Bcal readout
      • Comments on APD's (Serguei)
    • Updates on resolution studies (Blake)
      • have simulated pi0s in both geometries, have had compiling issues with analysis code the last week
    • Visit to Alberta
      • Schedule a phone conference for followup


Attending: UofR: George, Andrei, Zisis, Blake, Stamatis; IU: Matt, Claire, Brad (studying radiation on blocks); JLab: Beni, Tim, Elton, Elke; USM: Will

  1. Calibration
    • Filling Calibration Specification Table.
    • Zisis and George have added entries to the table.
    • IU meet internally and is discussing best numbers for table. Claire is studying how to calibrate the Fcal using pi0's. Based on results this will have an impact on the frequency and accuracy needed of a monitoring system
    • The requirements should be reviewed in a future meeting when all input is presented so that an informed decision can be made as to whether a single or multiple monitoring systems are required for the scintillating detector systems.
  2. Fcal
    • Progress on timing studies - Jake will report at the next meeting
    • Tim: Update on 64-block prototype? John has talked to local machine shops and has been reviewing specifications and schedules.
    • A detailed schedule for construction is being generated with FASTTRACK. Elke will send updated schedule with new procurement dates (which have been changed).
    • Matt inquired about the status of the magnetic shield sent to JLab. Tim' student will test in magnet, but will take a month or two. Matt's main interest is in feedback about steel specifications in shield and thickness requirement.
  3. Bcal
    1. Sipms: Decision on use of Getter#1 and no Getter units in the construction of arrays. Discussion
      • Summary of delivered units
      • Original plan was all Getter#1 devices. Sensl now proposes a 50/50 split, Elke has proposed 80/20 plit.
      • Elton had a concern that there might be an 80/20 split might not have sufficient statistics in the no Getter devices. Elke noted that for the pixellated arrays, we will have a total of 16 3x3 units, which is plenty of statistics.
      • Decision was made to request an 80/20 split. This implies that UofR and JLab will each receive five pixellated arrays and five summed arrays. For each set of five units, 4 will be fabricated with Getter#1 processing and one will be with no Getter processing. Elton will send this request to SensL.
    2. Bcal Sampling: Based on discussion, there will be no changes made to the lead thickness for the bcal modules.
      • Sampling studies (Stamatis) Media:Meeting271008.pdf. Report of work-in-progress. Three geometries studied:
        • Black: Thin lead
        • Blue: Hybrid (thin + nominal) lead
        • Pink: Nominal design lead
      • Resultion of hybrid module is about 15% lower than nominal at threshold at 16 degrees, difference decreasing at higher energy
      • Resolution of hybrid module is larger than nominal at 90 deg for Eg> 40MeV, difference increasing at higher energies.
      • Matt: Statistical gain is quantified, but systematic uncertainties are introduced by having different sampling fractions.
      • Zisis: There is already a division between inner and outer readout systems. The boundary between thin/thick lead would match a readout boundary.
      • Elton asked what checks would have to be made if a hybrid cal were selected. George and Zisis suggested the following minimal list:
        • Purcharse 3.5 mm lead sheets and verify that they can be properly swaged.
        • Produce a short stack calorimeter to check fabrication procedure. Lead times for Pb could be minimized by ordering Pb from England at slightly higher cost.
        • Delamination tests.
      • What is the downside to proceeding with the nominal design?
        • George: relieve pressure on photodetection efficiency of readout
        • Will asked about threshold. Elton: The threshold of the hybrid design should be able to be reduced by the improved resolution at threshold (~15% at 16 deg, ~5% at 90deg).
      • Matt: Studies that need to be conducted before a change of design is chosen:
        • Study systematics. Understand if different lead thicknesses lead to increase of systematics beyond that introduced by inner/outer readout sections
        • Study how the hybrid/nominal designs differ in reconstruction photons in the gap between Fcal and Bcal.
      • Comments by Will Brooks on Hall B thesis (see above).
        • See Fig 3.7b corresponding to inner Hall B calorimeter (about 6 rad lengths), 15 layers of 1 cm scint and 0.2 cm Pb. Thesis shows that for that study that the derived sampling fraction was relatively flat near the threshold of 100 KeV. We need to check what configuration (thresholds, step sizes, stack? parameters for secondaries, etc) is being used for the Hall D simulations.
    3. Readout: Serguei asked about the possibility of using APDs for the Bcal.
      • George: This option was studied early on. Low gain, and temperature stabilization were issues at that time.
      • It might be useful to see if any improvements in the technology change the picture for readout. We will ask Serguei to present an update at the next meeting.
    4. Resolution: Updates (Blake)
      • HDGEANT simulation of pi-'s, but have seg-faults. Elton indicated that if there are areas where he can use help, he should request it.
    5. Magnetic field. Zisis: Need to revisit the Bfield components in the region of the readout. (This has fallen through the cracks).
    6. Construction MOUs: Visit to Alberta
      • NSERC visits to Regina and Alberta this week.
      • Elton has a preliminary draft of a construction MOU. Will send to Regina for feedback toward the end of the week. Zisis reminded us that he and George will be at JLab Nov 6 and we can iterate on the MOU at that time.
      • Zisis has obtained rates for COOP students and other financial data as background information to the MOU.
      • Danny, Regina machinist, does not anticipate any difficulties in Ross machining the ends (as well as sides) of Bcal modules. They will visit Ross machining next week to review options. Requested that JLab make updated drawings available (including O-ring) for discussions. Tim will see if that can be fitted into designer tasks.