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Compton Photon Detector Upgrade

Compton Photon Detector Upgrade. Diana Parno 18 April 2009 HAPPEX Collaboration Meeting. Outline. Photon detector crystal upgrade GEANT simulations Tests at HI γ S Compton spectra Photon detector DAQ upgrade Preliminary results from d 2 n run. GSO Crystal.

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Compton Photon Detector Upgrade

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  1. Compton Photon Detector Upgrade Diana Parno 18 April 2009 HAPPEX Collaboration Meeting Diana Parno – 18 April 2009

  2. Outline • Photon detector crystal upgrade • GEANT simulations • Tests at HIγS • Compton spectra • Photon detector DAQ upgrade • Preliminary results from d2n run Diana Parno – 18 April 2009

  3. GSO Crystal • GSO crystal (6cm diameter, 15cm length) installed in Hall A in December • GEANT simulations suggest high efficiency • How much can we trust those simulations? Diana Parno – 18 April 2009

  4. HIγS Tests HIγS data Simulation • Visited High-Intensity γ Source (HIγS) • Tested GSO response to monochromatic photon beams at several energies • Results agree well with GEANT4 simulations • Limited by uncertainty in HIγS beam energy spread Diana Parno – 18 April 2009

  5. Compton Spectra Baylac et al., 2002 • Plotted as a function of photon energy ρ, the Compton cross section σ(ρ) is a parabola PbWO4 crystal (Saclay array) GSO Crystal Diana Parno – 18 April 2009

  6. Outline • Photon detector crystal upgrade • Photon detector DAQ upgrade • Triggered mode • Accumulator mode • Preliminary results from d2n run Diana Parno – 18 April 2009

  7. Triggered Mode • SIS 3320 FADC samples signal at 200 MHz • Write 512 preceding samples for every trigger • Quick collection of high statistics • Availability of individual pulses for study • Straightforward interface with electron detector • Trigger logic and .crl files developed at CMU and tested in Hall A • Thanks due to Fatiha Benmokhtar and Gregg Franklin Diana Parno – 18 April 2009

  8. Accumulator Mode Basics Accumulator 1 (Near) Pedestal Near Threshold Accumulator 2 (Window) Accumulator 0 (All) Accumulator 4 (Stretched Window) Far Threshold Accumulator 3 (Far) Accumulator 5 (Stretched Far) • FADC integrates signal for each helicity window • Signal size determines which samples contribute to each of six accumulators Diana Parno – 18 April 2009

  9. Accumulator Mode (continued) • From the raw accumulator data, we can extract a physics signal • Dilution-corrected asymmetry in physics signal tracks electron beam polarization Number of samples Average signal Average pedestal value Diana Parno – 18 April 2009

  10. Outline • Photon detector crystal upgrade • Photon detector DAQ upgrade • Preliminary results from d2n run • Extracting asymmetries • Cross-calibration with Møller measurements • Rates and linearity checks Diana Parno – 18 April 2009

  11. FADC Asymmetries: Consistency Check Diana Parno – 18 April 2009

  12. Towards a Beam Polarization • The Compton asymmetry Aexp is proportional to the electron beam polarization • We can cross-check Aexp with Møller results • Proportionality constant will be different for the two beam energies Diana Parno – 18 April 2009

  13. Rates • Compton photon rates of 3-5 kHz measured in scaler during d2n running (15 μA) • Agrees with rates measured in original DAQ • Rates well separated for cavity on/off states Diana Parno – 18 April 2009

  14. Linearity Check Edge at 7,400 Edge at 11,000 Edge at 23,000 Edge at 35,000 Diana Parno – 18 April 2009

  15. Future Work • Photon detector crystal • Detector response function • PMT linearity studies (Megan Friend’s talk) • Further tests at HIγS? • DAQ • Use multiplex buffers in FADC memory to reduce deadtime • First tests by Fatiha Benmokhtar and Wouter Deconinck • Preliminary results: DAQ rate > 10 kHz at CMU • Commission Accumulator + Triggered mode • Analysis • Refine asymmetry calculations • Fold in detector response function • Report beam polarizations! Diana Parno – 18 April 2009

  16. Thank you! Diana Parno – 18 April 2009

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