BCAL Readout Segmentation Task group Meeting: June 2, 2011

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Meeting Info

Time:

  • 11:30 JLab
  • 9:30 Regina

Location:

  • CC F326-327

Vid-con:

  • ESNet 8542553

Agenda

  • Review action items from previous meeting
    1. Confirm Sampling fraction number for BCAL (Zisis)
      • Done. Latest number from Stamatis' thesis is 9.5%
      • New number has been committed to calib directory in svn
    2. Decide on proper form of energy correction and recalibrate BCAL GlueX-doc-1301, Plot (Andrei)
    3. Check on status of SiPM cross-talk/after pulse separation (David)
      • Recent value of 15.7% reported for 1μs pulse
      • Spoke with Yi. Earlier measurements indicated ~12% for a 200ns gate.
      • Estimate for 100ns gate may be closer to 10% according to Yi's guess.
    4. Investigate addition to pedestal width due to gain variation of SiPMs in an array (David)
      • Yi pointed out that this will affect the signal width, not the pedestal width.
      • The measured gain variation between tiles is ~4%. Adding this in quadrature increases single PE signal width from 10% to <11%
    5. Update calibDB with most recent values for SiPM and BCAL properties (David)
      • Done 5/31/2011.
    6. Write up and distribute document describing how BCAL threshold is calculated based on event size (David)
    7. Check widths of energy distributions using low threshold and compare with expected (??)
  • BCAL Thresholds (David L.)

Minutes

Participants

David L., Elton S., Andrei S., Irina S., Zisis P.

Review of last week's action items

We reviewed the list of action items from last week's meeting and how each was addressed. Only a few generated discussion:

item 2:

  • Andrei showed some plots from his 2009 GlueX note indicating the sampling fraction is an energy/angle dependent quantity.
    • This will affect the ultimate resolution of the detector.
    • We discussed plans to develop a full map of the sampling fraction as a function of both incident energy and angle in order to include it in the simulation and reconstruction.
      • The amount of effort to do this will be non-trivial (i.e. > 1 week)
      • Some questions on how this will be incorporated effectively in the reconstruction of real data were raised
      • We will want to incorporate this effect in the simulation at some point, but given the amount of time we have to make a decision on the segmentation of the readout, it is unlikely this can be completed before then.
  • An additional plot was shown indicating the reconstructed energy distribution for 1 GeV photons
    • The four plots had the same data, but just showed different cut ranges. (Similar to plots shown last week)
    • The plots indicate that the reconstructed energy is systematically low. This addresses a comment in the minutes of the last meeting suggesting the systematic shift may only exist for low energy photons.
    • (Added by Elton): The systematic difference between reconstructed and generated energy is not due to incorrect sampling fractions, since the detector simulation puts the sampling fraction in by hand. We agreed that a new energy calibration should be done to see if this rectifies the systematic differences.

item 3:

  • We agreed that a cross-talk/afterpulse value of 10% was reasonable. This has already been entered into the calibDB.

item4:

  • The effective increase in width due to gain variation between tiles in an array was small enough that it will be ignored. No objections to this proposal were made.

item 6:

  • The wiki-page describing the calculation of the threshold based on dark hit rate and limiting the event size is available. It has not yet been reviewed.

'item 7:

  • No discussion

BCAL Thresholds

David presented 2 slides showing the results of threshold calculations based on the most recent, updated numbers and code.

  • Threshold for energy deposited on the far end of the BCAL for the fine segmentation scheme will have an effective threshold of 8.4 MeV
  • Threshold for energy deposited on the far end of the BCAL for the course segmentation scheme will have an effective threshold of 9.5 MeV (outer) and 8.8 MeV (inner)
  • Thresholds on the near end will be ~4 times smaller.
  • Dark hits will worsen the energy resolution of a single cell by 1-4MeV for the fine segmentation scheme
  • Dark hits will worsen the energy resolution of a summed cell by 2-8MeV for the course segmentation scheme

Action Items

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