July 21, 2008 Calorimetry

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  • The meeting will be held at 10:30 am ET
  • Phone:
    • +1-800-377-8846 : US
    • +1-888-276-7715 : Canada
    • +1-302-709-8424 : International
    • then enter participant code: 39527048# (remember the "#")

Reference Documents

  1. Previous minutes: July 7, 2008 Calorimetry
  2. Schedule, Tracker and Drawings (gluex pass)
  3. Schedule

References for the Alternative readout

  1. Response of FM pmts in magnetic field GlueX-doc-712
  2. Proposal for use of FM pmts in the outer section GlueX-doc-731
  3. Light collection in light guides GlueX-doc-1077
  4. Dependence of resolution on granularity GlueX-doc-659
  5. BCAL Geometry specifications, see Figure 3 of GlueX-doc-922
  6. BCAL Number of optical photons, see pages 4-7 of GlueX-doc-808
  7. Pi0 and eta mass resolution Physics and Calorimeter Performance Metrics Fig. 10


  1. Reports
  2. Updates
    • Calibration system
    • FCAL
    • BCAL
  3. Any other business


Attending: UofR: George, Zisis, IU: Matt, Mihajlo, JLab: Elton, Beni, Elke, Fernando; Athens: Christina

  1. Reports
    • Geometry updates (Beni)
      • Now in the Repository are: 8mm Aluminum inside plate, FDC cables running upstream
      • Current studies by Matt and Blake on 3x3 and 6x4 readout without the above materials.
    • Shower reconstruction (IU)
      • Comparison of 3x3 vs. 6x4 BCAL Inner Segmenation
      • Beni will send an e-mail with information to newest xml files with Al plate and FDC cables upstream. These will be used by Blake to repeat resolution studies with up-to-date geometry.
      • Results of Present Studies (Matt). Main changes include increasing the threshold by a factor of 2 (realistic threshold). Photons are generated in the target. Showers are included in study non-interactin photons are found and reconstructed within 3sigma of the generated energy. Resolution was determined for the 6x4 and 3x3 configurations. PLots were shown for resolution in costhe, phi, and energy. Generally the costhe resolution is better for the 6x4 configuration, about 50% better for phi. However the 3x3 configuration gives improved energy resolution. The cell threshold used was about 5 MeV (at end of module after attenuation), or about 10 MeV at the center of the module. In addition there is a 30 MeV shower threshold. Time smearing has been included in the simulations. There could be some residual systematics in the present analysis.
        • Preliminary conclusion is that the geometry has not changed much since "winter 2008", although cables are now in.
        • Matt: The degraded energy resolution is likely due to the loss of photons for cells that have less than the minimum number required in the shower reconstruction (5-10 MeV).
        • Beni will point to updated files with Al plate and cables routed upstream. With the new geometry the improved thresholds should also be simulated. The lower threshold expected for FM PMTs is not in yet either. Estimates of this threshold should be included in the upcoming studies.
      • Elton asked about the considerations for less granularity in the outer section.
        • Christina: The proposal is to segment the outer into a 2x1 (segmentation in depth, not phi), reading out each segment with a 2" FM PMT, largest available. This is due to the relatively small number of p.e. expected for the outer region. Reference the work from GlueX-doc-731 which discusses the option for a 2x1 segmentation in the outer Bcal Sector. GlueX-doc-712 reports on measurements of the fine mesh PMTS in the magnetic field.
      • Non-linear photon energy corrections in the FCAL
        • Non-linear response in the Fcal is parameterized more precisely. Reconstructed showers give energy resolution ~ 5.4%/sqrt(E) + 0.2%. The contribution of photostatistics to the statistical term is 3.5% (assumes improved light collection and better light yield).
        • Elke: Does the simulation include the new F100 rad hard glass? No. But reduced transmission could be included in an average way into the calorimeter response by increasing the 3.4% by sqrt(2). Corrections to the shower profile for the light attenuation in the block should be studied as some point.
    • Discussion on resolution of various options
      • George: PMT saturation needs to be considered when granularity is reduced.
      • Elton: Optimum granuarity for SiPMs may be closer to 4x4 (instead of 6x4). George agreed, indicating simulation of physics channels show that the high energy showers are likely inpacting the Bcal at low angles where their energy profile will likely not reach layers 5 and 6.
  2. Updates
    • Calibration system
      • Calibration meeting scheduled for Tues Aug 26 at 10:30. Documentation will be prepared in advance to provide background to the discussion.
      • Difusors have been obtained from CERN and will allow operation of PMTs at higher gain for future tests
      • Fifty cards with LEDs are expected for use in tests.
    • FCAL
      • Jake has started putting together the 3x3 array, which will be flashed with a fast LED.
      • Flash ADC readout is being checked. Trigger signals and CODA are running. Code to readout Flash is being written/debugged.
      • PRIMEX meeting indicated that machined soft iron shields (square off edges). Effect of machining on magnetic properties needs to be understood. Elke said that if a sample is shipped to JLab, it can be tested in a magnetic field. John will send one sample.
    • BCAL
      • preparations for fiber testing. Measurements of Npe for 2m fiber is in progress. Will report as soon as mesurements are complete.
      • At the moment it appears that the number of p.e. measured for the fibers is about 2 times lower than what we require in the spec. We need a procedure for testing and qualifying fibers from St. Gobain and Kuraray.
      • SiPM PDE vs DR
        • At the last sipm meeting, Padraig conceeded that the current SiPMs are not likely to meet our requirements. He suggested that this could be accomplished with additional cooling, or with the next generation of SiPMs. On the face of it, cooling might achieve our PDE/DR requirements, but addiitonal mechanical and electrical issues need to be considered for such a setup. No decisions are taken yet, but data is fairly consistent. SensL is still planning to deliver the A35H 3x3 mm2 SiPMs at the beginning of Aug and these will be tested for comparison with other samples.
  3. To do:
    • Identify files with new geometry (Beni)
    • Estimates of pedestal width (electronic noise, etc.) for FM PMTs. The dark rate should be negligigle in this case.
    • Resolution studies with up-to-date geometry (Blake)
    • Resolution studies with different segmentation for the outer section.
    • Add F100 rad hard glass to simulation.
    • Calibration meeting Tues Aug 26
    • Decision on Bcal sampling fraction needed by Sep.