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

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

3. Diana Parno – 18 April 2009 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?

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

5. Diana Parno – 18 April 2009 Compton Spectra Plotted as a function of photon energy ρ, the Compton cross section σ(ρ) is a parabola Baylac et al., 2002 PbWO 4 crystal (Saclay array)GSO Crystal

6. Diana Parno – 18 April 2009 Outline Photon detector crystal upgrade Photon detector DAQ upgrade –Triggered mode –Accumulator mode Preliminary results from d 2 n run

7. Diana Parno – 18 April 2009 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

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

9. Diana Parno – 18 April 2009 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 pedestal value Average signal

10. Diana Parno – 18 April 2009 Outline Photon detector crystal upgrade Photon detector DAQ upgrade Preliminary results from d 2 n run –Extracting asymmetries –Cross-calibration with Møller measurements –Rates and linearity checks

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

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

13. Diana Parno – 18 April 2009 Rates Compton photon rates of 3-5 kHz measured in scaler during d 2 n running (15 μA) Agrees with rates measured in original DAQ Rates well separated for cavity on/off states

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

15. Diana Parno – 18 April 2009 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!

16. Diana Parno – 18 April 2009 Thank you!