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Compton Electrons

Compton Electrons. Dipangkar Dutta & Jeff Martin Mississippi State & University of Winnipeg. 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].

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Compton Electrons

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  1. Compton Electrons Dipangkar Dutta & Jeff Martin Mississippi State & University of Winnipeg

  2. 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

  3. Compton Survey(focusing on electron detection) others: NIKHEF, VEPP-3, VEPP-4, SPEAR, CESR, DORIS, PETRA, HERA trans., LEP

  4. 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 don’t intend to) • background rates highly dependent on energy and beam tune [Nanda, Hall A]

  5. Rates Hall-A: Signal rate : 5KHz for 8mA current @ 500W (energy independent) Background : @ 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

  6. 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 R&D project on its own.

  7. Si cost estimate (C. Davis, et al 2005 NSERC submission) Note: RTI category 1 limit is $150 kCAD.

  8. 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)

  9. 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)

  10. 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.

  11. 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 20~100 mm 400 pixels ~ 8 mm Depletion region ~ 2 mm First developed and produced by CPTA Russia. Now also Hamamatsu Photonics Substrate

  12. Performance

  13. 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

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