Sep 2, 2008 Calorimetry

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Items for followup from Aug 18 meeting

  1. George: report on trip to Edmonton
  2. Estimates of pedestal width (electronic noise, etc.) for FM PMTs. The dark rate should be negligigle in this case.
  3. Resolution studies with up-to-date geometry (Blake) ONGOING
  4. Resolution studies with different segmentation for the outer section. - LOWER PRIORITY
  5. Add F100 rad hard glass to simulation. - Matt will do this
  6. Decision on Bcal sampling fraction needed by Sep. - Work by Stamatis (on vacation) will be summarized upon his return.

Documents to Review

  1. Please place documents here for review in advance of meeting
  2. Calibration-Monitoring
  3. Paul Smith's Fiber Pulser

Tentative Agenda

Note: This meeting will be dedicated to reviewing calibration issues. Other reports will be included as time permits.

  1. Announcements
  2. Review of Calibration Issues
  3. Reports
  4. Updates
  5. Any other business


Attending: Athens: Christina, George, Pavlos; UofR: Zisis, George, Kathryn, Blake; JLab: Elton, Beni, Tim, Fernando; IU: Matt, Mijahlo, Claire Tareert; FIU: Werner.


  • Claire Tarbert is a new research associate at IU. Welcome!

Review of Calibration System

  • Athens update report: GlueX-doc-1092
  • Christina went over the posted presentation
  1. First the laser option was presented
    • APD used to monitor the absolute light from the laser, but noise pick up from the laser was a problem. Elton indicated that a full shield was necessary to shield the laser. Method for shielding similar laser can be found on the bottom of page 3 of Hall B CLAS-NOTE 91-002.
  2. Second, the LED option was presented.
    • 2x1 cm2 boards with the LED and pulsing electronics have been made; 35 boards produced.
    • The idea is to place the boards near each pmt to be calibrated, e.g. on the light guide of the SiPMs. George: could be placed on the tapered length of the guide.
    • Fernando asked about the temperature dependence: it has not yet been measured.
    • Control board (for about 30 LEDs) has been constructed and would be placed about 2-3 m away from the LED.
    • Each channel requires three cables (voltage, trigger signal and ground). The trigger signal is a TTL pulse.
    • Question about masking individual channels for firing? This would check (optical) cross talk between channels.
  3. The calibration system needs to have its requirements clearly defined. Each subsystem (Fcal, Bcal, Start counter) reviewed its requirements, but further refinement is necessary.
    • Elton prepared the following table to clarify the requirements. We need to complete it to provide adequate feedback to Athens:

Calibration Specifications Table

DRAFT Table of Calibration Specifications: Blanks need to be completed by subsystem.
Characteristic Fcal Bcal TOF Start
Light uniformity channel-to-channel ≤ 15%
Dynamic range of input (number of photoelectrons) typically 100 100 up to 800
Requirement on absolute light input none (PRIMEX might have) 150 pe on module
Variation in arrival times of cal pulses ~3 ns ≤ 2 ns ~3ns ~3ns
Time stability gain and timing (one channel) ≤ 10% in 6 months
Temperature stability (likely cause of time stability) 1o causes 3% gain change
Location of calibration input From front to monitor rad damage light guide tapered side
Geometrical constraints Approximately 90% of front 4x4 cm2 area available packing of WC and LGs, LED fitting, cable routing

  1. Comment: Time (and temperature) stability most important.
  2. Comment: Option of delivering a range of light intensities important (e.g. using various filter settings).
  3. Comment from Werner: The flexibility in the use of the LED would be very useful for the start counter. Christina: Still need to test stability.
  4. Questions to Matt: What uniformity could one expect from the plexiglass input system? How many fibers were used to pulse the plexiglass, i.e. how often were they spaced?
  5. Comment: Matt drew attention to an LED pulser by Paul Smith which might be a useful reference.

Fiber Measurements

  1. Fiber Test Stand at JLAB (Beni)
    • Test setup now operational . Attenuation length and light output completed for Kuraray and recent Bicron Fibers. More measurements under way.
  2. Fiber Tests at Regina (Kathryn)
    • Light output reported for Kuraray and Bicron fibers. Measurements of attenuation lengths will be summarized and included along with light output measurements.
  3. Preliminary conclusion is that Kuraray fibers have higher light output and longer attenuation length, but results still need to be digested.
  4. George noted that a couple of Quantacon pmts would simplify and give confidence to the calibration procedures.