PREx%20detector

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PREx detector status report
Piotr Decowski Smith College
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HRS focal plane
Keith Otis, UMass
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Quartz stack
Thin quartz
Keith Otis, UMass
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• Requirements
• Integrating
• Radiation hard (1 GHz)
• Good resolution (lt25)
• Small size

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Test bench for cosmic ray measurements
Cosmic muon Egt300 MeV
quartz block stack
Quartz blocks
5 cm
Trigger scintillators
Cherenkov light
5 blocks
Number of Cherenkov photons
3 blocks
20 cm
300 MeV
PMT
1 block
Pb 20cm
trigger scintillators
Muon energy (GeV)
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Response of Hamamatsu R329-02 PMT to
single photons at HV 2000 V
shutter
LED
200 ns 1 kHz
LED power pulse
1100 optical filter
PMT
PMT output
2000 V
ADC gate
29 channels
29 channels
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Cosmic muons - measurements
1 block 5cm4cm0.5cm
5 blocks
Number of channels per PE 29
Measurement
Measurement
Channel
Channel
Simulations
Simulations
of photons
of photons
Factor of 4 puzzle Nph in simulations NPE in
measurements
Measurement
Simulations reproduce well width of
the experimental distributions
Simulations
Black dots Distr. of events vs (channel / number
of channels per PE) (meas.) Red dots Distr. of
events vs number of photons reaching PMT
(simulations)
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Simulations
Distributions of Cherenkov photons generated in
quartz blocks of different thicknesses
Number of photons and RMS vs block thickness
RMS
N of photons
RMS 39
RMS 11
1cm block
15cm block
Quartz block thickness (mm)
Distribution of generated photons
THINNER BETTER!
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Do we need scanners?
Examples of scans from HAPPEX II
Scanners are very useful for precise monitoring
of electron flux distribution at the detector
face. Good knowledge of this distribution is
important for determination of the average Q2
value (note that it is critical because of the
small size of PREx detector)
James Barber, UMass
Momentum axis
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Scans parametrized
Logarithmic distribution fitted with polynomial
a0
a1
a3
a2
a4
Run number
James Barber, UMass
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• Plans for the nearest future
• Optimization of quartz block size, and of
• light collection using cosmic muon setup
• Mechanical design and machining
• of detector prototype
• 3. Test of prototype using CEBAF electron
• beam (summer 2007?)