Notes of Cal working group meeting uploaded.

[Elton Smith <elton@jlab.org>]

Hi all,

I have uploaded minutes to yesterday's Cal Working group meeting. The text
is also given below. Comments/suggestions --> edit wiki.

Cheers, Elton.
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=Minutes=

# Attending: JLab: Beni, Elton, Fernando, Eugene, Tim, FIU: Werner, UofR:
Zisis, Blake, Kathryn, George, Andrei; IU: Mijahlo, Brad, Claire, Matt.
# Cooling of BCAL Readout [moved forward due to accomodate Tim's schedule]
#* Tim presented a preliminary concept for cooling the SiPMs
[http://argus.phys.uregina.ca/cgi-bin/private/DocDB/ShowDocument?docid=1233
GlueX-doc-1233 DRAFT Cooling Concept]
#* Based on JLab informal discussions.
#* Idea is to directly cool the sensor via Peltiers to 5deg C with a
cooling circuit at room temperature to remove the heat generated by
Peltier (~1.5 Watt/channel).
#* SiPM geometry based on SensL ceramic design which allows cooling sensor
directly by offsetting electronics via long pins.
#* Peltier junction and sensor would be potted to prevent condensation on
sensor. Potting is needed to have sufficient insulation to confine cold
area.
#* Should provide a concrete basis for further discussion.
#* Matt: Mentioned that CLEO had good success with the following scheme
for cooling their drift chamber electronics: Fill space with (dry) N2. Use
polyethelne tubing with cooling liquid (PF200) to cool N2. System was
robust and inexpensive.
# FCAL Update
## [[FCAL Magnetic Shield Design]]
##* New rectangular magnetic shield mechanical prototype is under
development. Allows more space for electronics
##* This gets the design away from the flex boards which were fragile and
costly
##* New design would have 3 PC boards: one for control, one for HV and one
with connections. The HV part was the lest reliable. This design would
ease maintenance of that particular board.
##* Elton: Check to make sure that there is sufficient space between
grounds and (negative) HV. Gradients can lead to small ion mobility in the
glass and deteriorate photocathode. Will try to dig up some references.
## John has finished glass support drawings and sent them to Tim.
## Would like to see the results of field calculations for new design to
evaluate impact on pmt performance.
# Simulations
## Simulation of BCAL Threshold:
[http://argus.phys.uregina.ca/cgi-bin/private/DocDB/ShowDocument?docid=1231
GlueX-doc-1231] (Matt)
## BCAL Dark Hits (Matt)
##* [[Media:Res_vs_dkrate.pdf | Resolution Dependence on Dark Rate]]
##* [[Media:Dark_rate_pi0_compare.pdf | &pi;<sup>0</sup> Peak for
Different Dark Rates]]
##* Adjusted threshold settings for an occupancy of 5%.
##* Evaluated resolutions based on realistic GEANT simulation and
reconstruction.
##* There are two effects due to increased rates: 1) dark rate increases
and 2) threshold are increased. Both affect resolution.
##* These studies show that our nominal goals of 40 MHz affects resolution
only slightly, but rates of 160 MHz have substantial impact on resolution
and reconstruction. These studies support our goals for PDE/dark rate
goals.
##* Note to Blake: It is likely that the calibration will change at low
energies and further studies will require a re-calibration.
# BCAL Update
## Preparations for construction
##* Small contract will cover the production prototype (49th module)
##* Contract will include construction manager as well as fabrication of
48 modules
##* Purchase Reqs are nearly ready for submission.
## Results of Fiber Tests
##* Elton: First article fibers have been approved and Kuraray has been
directed to proceed with production. Even though there are systematic
differences between JLab and Regina measurements, all results point to
Kuraray satisfying our specifications. See [[Image:Hamamatsu pages.pdf]]
Guidelines from Hamamatsu
### [[Kuraray Fibre Tests| Kuraray Fibre Tests - Regina]] - updated
(Blake)
###* More fibers have been measured. Attenuation lengths are uniform
between samples (~450 cm) and reproductible, but higher than those
measured by Kuraray and JLab.
### [[Kuraray No of pe - April 2, 2009]] - updated (Andrei, Kathryn)
###* Andrei described procedure for the measurement of absolute number of
photoelectrons. 90Sr source placed at midpoint of fiber, 200 cm away from
a SiPM on one side and 200 cm away from calibrated pmt on the other. PMT
was used as trigger and SiPM spectra was evaluated. Result was a number of
about 5.5 p.e. in response to the source.
###* The SiPM spectra was corrected for triggers unrelated to source.
###* The threshold of the PMT on the extracted number of photoelectrons
was studied and reduced the number by about 0.3 p.e.
###* Zisis will send a reference to similar fiber studies by COMPAS.
## Note: Box of fibers bound for Regina was crushed. Half of the samples
from the box were shared between JLab and Regina. There is agreement that
the fibers in the damaged box were not affected.

# Review of Action Items