Detectors for PREx

1
Detectors for PREx
Piotr Decowski, Smith College Krishna Kumar. UMass
Collaboration Meeting, April 17-18, 2009
2
January 2008 test
Dustins analysis
Statistics
0.5cm thick quartz
1cm thick quartz
Pedestal width 1.85
MPV 25.48 GSigma 5.65 Net width 5.34
(21) Net RMS 8.57 (34) (5.34)2 28.5
MPV 14.37 GSigma 4.59 Net width 4.20
(29) Net RMS 5.49 (38) (4.20)2 17.64
NPE 1/(.21)2 22.7
NPE 1/(.29)2 11.9
3
January 2008 test
Absolute determination of NPE
NPE (1.60210-19 C)PMTGain
MPV(ch)(5010-15C/ch)
LeCroy 1881M ADC
NEEDED!
4
Measurement of PMT gain
Anna Boehle, Diana Jaunzeikare,
Smith College
21 fC/ch
5
Measurement of PMT gain, cont
PMT Hamamatsu R7723Q (fused silica window)
PMT ZK40033 Gain _at_ -2000V 4.384105
6
Results
1cm thick quartz
0.5cm thick quartz
NPE 11.9
Statistics
NPE 22.7
NPE (1cm)/NPE(0.5cm) 1.90
Absolute gain
NPE 18.1
NPE 10.2
NPE (1cm)/NPE(0.5cm) 1.77 (exp)
Note without pedestal width subtraction
statistics gives NPE(1cm) 20.3, and NPE(1cm)
9.8
7
GEANT4 Simulations
Jon Wexler, UMass
Cone mirror
Tube mirror
PMT cathode
Quartz block
8
Simulations photon energy range
PMT QE
380nm Alzak cut
Standard PMT QE cut
185 nm Quartz cut
500 nm QE cut
Alzak reflectivity 93 - 98 Anodized Al
reflectivity 85 - 87
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Simulations results
1cm thick quartz
0.5cm thick quartz
NPE 26.6
NPE 13.9
Sim
NPE 22.7
NPE 11.9
Stat
NPE 18.1
NPE 10.2
Gain
Simulations overestimate experimental results by
30 (there is room for improvements!)
10
Simulations Al vs Alzak
1cm thick quartz
0.5cm thick quartz
NPE 26.6
NPE 13.9
Alzak
NPE 64.5
NPE 34.0
Al
Improvement factor 2.4 !
11
HRS focal plane
Bob Michaels
12
Detector concept
Top view
LED
2 PMT
Optimize
10 cm
Optimize
2 PMT
Expected 20 PE per PMT/electron (4nA _at_1GHz)
Quartz 0.5cm (0.25cm) thick
Al mirror tube
Two stacked 0.25cm thick detectors?
13
Detector configuration
A_T Det
Det 2
Det 1
e- beam
e- beam
14
Conclusions and plan

• Simulations are reproducing experimental data
  well.
• We have tool to optimize geometry of new
  detectors
• with larger quartz accommodating larger
  footprint of
• the Pb elastic peak.
• Use of anodized aluminum instead of Alzak and
  PMTs
• with fused silica window significantly
  increases number
• of PEs.

• Plan for nearest future
• Construction of two prototypes of detectors with
  existing
• quartz blocks to test PE enhancement due to
  Al mirrors.
• These detectors will be used at the
  beginning of the HAPEX run.
• Optimization of geometry of detectors with larger
  quartz blocks.
• Construction of A_T detectors (similar to used in
  the January 2008
• tests).
• Construction of small plastic scintillator pads
  which will be
• mounted above the main detectors, and in
  counting mode
• will substitute S0 detector.