PREx detectors

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PREx detectors

• Progress report

Krishna Kumar Keith Otis UMass
Piotr Decowski Selamnesh Nida Smith College
Collaboration Meeting, May 17-18,2007
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HRS focal plane
Keith Otis, UMass
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Thin detector

• Requirements
• Integrating
• Radiation hard (1 GHz)
• Good resolution (lt25)
• Small size

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Challenges

• PM output signal per one electron passing the
  detector

Relative error
Simulations
Binominal distribution
Relative statistical error of the parity
violating asymmetry
To minimize we have to maximize
and
For we need
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However
For (
) and expected rate of electrons 1 GHz, the
current at the PM output will be
We need a very low gain, linear tube!
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Thin Quartz Detector
Concept
15 cm
conical mirror
4 cm4cm
2 3
PM
quartz
tube mirror
Optimization -- cone length (mirror angle) --
quartz thickness -- quartz position in the cone
-- PM diameter (2 and 3)
Electron energy 850 MeV
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Cone length (5 mm quartz)
39
d2mm
d10mm
d5mm
2 inch PM
d5mm
d2mm
d10mm
.162
6 cm
6 cm
Optimal choice 2 inch PM, 6 cm cone, d 2 mm
Number of photons reaching PM
Relative width of distributions
Cone length (cm)
Cone length (cm)
50
3 inch PM
.14
7 cm
7 cm
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Quartz thickness
4 mm
15 mm
onset of showering
3 inch PM
rms of full distribution
Optimal choice 5 mm quartz block
Relative width of distribution
Average number of photons at PM
2 inch PM
peak width
5 mm
5 mm
Quartz thickness (mm)
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Optimal detector parameters
Trapezoidal quartz block 0.5cm thick, 4cm4cm
upper surface Cone mirror 6 cm long, with quartz
block positioned at the smaller opening of the
cone 2 inch diameter PM
The design is robust - the resolution does not
depend strongly on design parameters as well as
condition of quartz surface (as a matter of fact,
more rough surface improves resolution by 1)
Simulated performance NPh 40, ?NPh 17
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Design concept
Tube mirror
Cone mirror
to PM
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Realization
Front tube
Quartz
Quartz holder
Cone
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Plans
Thin detector

• Drawings of the detector parts are in an advanced
  stage
• Two prototypes will be built during this summer
• First beam tests planned for fall 2007 (in the
  Moller target area)

Stack detector

• 4 - 5 quartz blocks 0.5cm - 1cm thick separated
  by tungsten radiator
• Simulations of optimal design (in progress)

Important issue choice of proper photon
detector for high intensity runs