Compton Electrons

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Compton Electrons

• Dipangkar Dutta Jeff Martin
• Mississippi State University of Winnipeg

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Compton Recoil Electron Kinematics

• Struck electron loses energy equivalent to photon
  energy increase. Very little angular deflection.
• At 850 MeV, max energy loss is E? 25 MeV
  Bates.
• Struck electron is momentum analyzed using
  downstream dipole magnet.

e.g. Mainz Compton
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Compton Survey(focusing on electron detection)
Location Beam energy Photon Det. Electron Det.
Hall A 1.0 6.0 GeV PbWO4 silicon
Mainz 0.1 0.9 GeV NaI SciFi
SLAC 45.6 GeV W / quartz Pb / gas C
HERA Long. 27.5 GeV NaBi(WO4) none
Bates 0.3 1.0 GeV CsI none
others NIKHEF, VEPP-3, VEPP-4, SPEAR, CESR,
DORIS, PETRA, HERA trans., LEP
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Typical Requirements forElectron Detector (Mainz
Hall A)

• 0.5 mm spatial resolution in dispersive
  direction
• high efficiency (no gaps)
• high rate capability (up to 100 kHz)
• rad hard
• Notes
• Both Mainz Hall A use CW laser operation (we
  dont intend to)
• background rates highly dependent on energy and
  beam tune Nanda, Hall A

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Rates
Hall-A Signal rate 5KHz for 8mA current _at_
500W (energy independent) Background _at_ 2GeV is
2KHz (depends on beam
tune) Hall-C Laser
power is ave. 90W with duty factor
of 0.15 Signal rate 15-20KHz at
180mA Background low (scaled from Hall A rates)
- Thanks S. Nanda
Multiplicity 1.5 per pulse
- Thanks Dave
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Technologies Under Consideration for Hall C
Compton

• Silicon
• advantages proven technology (Hall A),
  acceptance easy to understand, rad hard.
• disadvantages slow? potentially high
  electronics costs.
• SciFi
• advantages fast, cheap, use Si-PM readout
• disadvantages rad hardness? more difficult
  acceptance?
• alternate quartz fiber same readout, very rad
  hard.
• GEM
• advantages cheap, rad hard, fairly fast.
• disadvantages electronics costs hard to
  estimate, potentially complicated RD project on
  its own.

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Si cost estimate (C. Davis, et al 2005 NSERC
submission)
Item Cost (kCAD)
Si detectors (8 x PIPS-S-8) 44
Electronics _at_ 192 channels 82
Cooling 8
Misc 2
Travel 10
Total 146
Note RTI category 1 limit is 150 kCAD.
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Options for Fiber Based Recoil Electron Detector

• Scintillating Fiber Based Device
• (SciFi, e.g. Mainz Compton)
• Quartz Fiber Based Device
• (e.g. SLAC Compton -photon detector, 25m
  resolution)

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SciFi Based Electron Detector
SciFi available from 3 manufacturers Bicron,
Kuraray Pol.Hi.Tech.
Typical light yield 4.5 p.e./mm, for 1mm diameter
fiber. Achieved resolutions of 125mm. Kararay
is the most radiation hard no damage detected
when exposed to 1Mrad (tested with e- beams).
E. C. Aschenauer et al. hep-ex/9710001
We have not found any noticeable change in the
detector properties over time.
-Yoshio Imai (Mainz
Compton)
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Quartz Fiber Based Detector
Signal through Cerenkov radiation, thus low
photon yield (only few of photons is trapped) 1
pe/GeV/cm. Also incidence angle dependent. But
25mm resolution achieved at SLAC, extremely
radiation hard 2 Grad, insensitive to
soft synchrotron radiation and high linearity.
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Light Detection
Mainz used Multi Anode PMTs made by Hamamatsu
SiPM the new kid on the block
Silicon Photo Multipliers - densely packed array
of Avalanche Photo Diodes (1000 in a 1mmx1mm
grid) operating in Geiger mode (i.e. individual
photo-electrons from each micro pixel cannot be
distinguished).
1 mm
20100 mm
400 pixels
8 mm
Depletion region 2 mm
First developed and produced by CPTA Russia. Now
also Hamamatsu Photonics
Substrate
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Performance

PMT SiPM
Gain 106 105106
Photon Detection Efficiency 0.1 0.2 0.1 0.4
Response fast fast
Photon counting Yes Great
Bias voltage 1000 V 30 70 V
Size Small Compact
B field Sensitive No influence
Cost Not low Low (10)
Dynamic range Good Not so good
Stability Good Unknown, maybe good
Noise (fake signal by thermions) Quiet Noisy (order of MHz) can reduce by cooling
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Roadmap to First Light

• Decide technology ASAP
• Base decision on
• rates (signal and background)
• granularity (guess similar to Hall A and Mainz?)
• fiducializability?
• Current favorite ? Input from
  collaboration/experts?
• Begin detailed budgeting for upcoming grant
  cycles
• NSERC deadline end of Oct.
• DOE deadline Nov.
• Need ideas on how to split tasks (MSU vs.
  UWpg/Canadians)
• Detailed simulations decide position wrt
  chicane dipoles.
• Prototyping
• Receive funding
• Build it