1. ArgonneResult_2004-02-07.ppt1 Results of PoGO Argonne Beam Test PoGO Collaboration meeting at SLAC, February 7, 2004 Tsunefumi Mizuno mizuno@SLAC.Stanford.EDU History of Change: December 10, 2003 first written by T. Mizuno February 6, 2004 updated by T. Mizuno

2. ArgonneResult_2004-02-07.ppt2 Experimental Setup(1) beam direction x y Objective: to examine the performance of PoGO and verify the Geant4-based Monte-Carlo Simulator with a PoGO prototype PoGO: 200-400 units of fast/slow plastic scintillators and BGOs Prototype: 7 units of fast scintillators (detection part) Polarization vector was along the horizontal axis (x-axis) Irradiated polarized synchrotron beam of 60 keV, 73 keV and 83 keV at the center of the central scintillator. The same beam was used to calibrate the energy response. Rotated the detector in x-y plane in 15 degree steps.

3. ArgonneResult_2004-02-07.ppt3 Definitions polarization vector 30degree y x Beam Direction 12 345 67 We defined that xy plane is normal to the scintillator principle axis. Scintillators are numbered from 1 to 7. Central scintillator is number 4. Beam goes from +z to -z. Polarization vector is along x-axis. We rotated the detector. When we rotated it by 30 degree, scintillator number 2 was along the y axis.

4. ArgonneResult_2004-02-07.ppt4 Experimental Setup(2) Ring scintillators central scintillator The data acquisition was triggered by the coincidence of hits in the central scintillator and any one of ring scintillators. Shaper outputs were digitized and recorded by a waveform analyzer. During the test we found that the coincidence efficiency was not 100% and varied among channels. -> We also took ch4-only-trigger data to evaluate the relative efficiency.

5. ArgonneResult_2004-02-07.ppt5 Data Files 212 data files and the log (txt and pdf format) can be obtained through the web: http://www.slac.stanford.edu/~mizuno/PoGO/Argonne/index.html “Digitized data files”, where peak voltage is converted in 10 bit integer are used in the following analysis. Data files are also available via ftp: ftp as 'anonymous' to ftp.slac.stanford.edu then "cd groups/astro_gam/PoGO/Argonne”

6. ArgonneResult_2004-02-07.ppt6 Run Summary Coincidence Trigger (in 15 degree steps): run048-073: 83.5 keV run run106-149: 60.2 keV run run164-190: 73.2 keV run Ch4 Trigger (in 30 degree steps. They don’t cover the whole azimuth angle): run191-197: 73.2 keV run run210-212: 83.5 keV run Calibration Run: run088,090-096: 83.5 keV run run090-105,150-156: 60.2 keV run run157-163: 73.2 keV run For more details, please read the log in http://www.slac.stanford.edu/~mizuno/PoGO/Argonne/index.html. http://www.slac.stanford.edu/~mizuno/PoGO/Argonne/index.html We also took the BG data but does not use them in this report. BG is small and does not affect the results very much.

7. ArgonneResult_2004-02-07.ppt7 Calibration Run Fitted data with gaussian + linear function Below we list the peak position, energy resolution and channel/energy conversion factor of 73.2 keV beam. We use these conversion factors in the following analysis. (They agree with the conversion factors obtained for 83.5 keV and 60.2 keV within 2%.) ch1: p=326.5, sigma=34.9 (FWHM:25.1%), f=4.46 ch2: p=331.5, sigma=32.3 (FWHM:22.9%), f=4.53 ch3: p=334.9, sigma=39.5 (FWHM:27.7%), f=4.58 ch4: p=317.7, sigma=41.5 (FHWM:30.7%), f=4.34 ch5: p=350.9, sigma=49.1 (FHWM:32.9%), f=4.79 ch6: p=326.0, sigma=35.5 (FHWM:25.6%), f=4.45 ch7: p=377.2, sigma=43.6 (FHWM:27.2%), f=5.15

8. ArgonneResult_2004-02-07.ppt8 Geant4 vs. EGS4 We have compared the polarized Compton scattering between Geant4 and EGS4, and found that G4 gave less asymmetry. Y. Fukazawa at Hiroshima Univ. independently compared two simulation toolkits, found the difference and fixed Geant4. Geant4 with the fix agrees with EGS4 in ~10%. This possible minor bug was already reported to Geant4 team and to be verified. (it was ~15% without “fix”) Simulated modulation curves observed by PoGO (geometry is simplified) for Crab spectrum in 25-200 keV.

9. ArgonneResult_2004-02-07.ppt9 73.2 keV Ch4 Trigger Run (1) Event selection criteria: Detection threshold was 2 keV 2 scintillators detected a hit (one was the central scintillator) Deposit energy of the central scintillator was below 40 keV and less than half of the total deposit energy. 45 keV <= total deposit energy <= 100 keV Total deposit energy seems to be ~70 keV, a little bit smaller than the beam energy. deposit energy in the central scinti. (keV) Total deposit energy (keV)

10. ArgonneResult_2004-02-07.ppt10 73.2 keV Ch4 Trigger Run (2) ch1 ch7 ch3 ch5 ch2 ch6 Modulation Factor ~(1700-650)/(1700+650) ~44.5%

11. ArgonneResult_2004-02-07.ppt11 Trigger Efficiency (1) During the beam test, we found that the trigger efficiency is not 100% for coincidence trigger run and it varies among channels. E.g., efficiency of ch6 seemed to be ~2/3 of others. To obtain “unbiased” events, we performed ch4 trigger run, and the results were shown in page 9. By comparing them with the coincidence trigger run of the same energy and rotation angle, we can evaluate the relative trigger efficiency of each channel.

12. ArgonneResult_2004-02-07.ppt12 Trigger Efficiency (2) ch1 ch3 ch5 ch2 ch6 Use 73.2 keV runs. Efficiency of ch7 is normalized to 1. Errors shown are statistical errors only. Fitting by constant (dof=5): ch1:0.843+-0.017, chi2=6.6 ch2:0.979+-0.021, chi2=8.7 ch3:0.987+-0.021, chi2=6.1 ch5:0.803+-0.018, chi2=5.7 ch6:0.621+-0.013, chi2=7.6 Chi2/dof>=1. Probably there are systematic errors comparable to statistical ones.

13. ArgonneResult_2004-02-07.ppt13 73.2 keV Coincidence Trigger Run(1) Selection criteria are the same as those for ch4 trigger run. Total deposit energy seems to be a little bit smaller than beam energy. We observed a small dip around 10 keV in energy deposition in scintillator #4. This dip is more prominent in coincidence with ch1, ch5 and ch6, where the trigger efficiency is low. -> The dip could cause the trigger inefficiency. Total deposit energy (keV) deposit energy in the central scinti. (keV)

14. ArgonneResult_2004-02-07.ppt14 73.2 keV Coincidence Trigger Run (2) ch1 ch3 ch5 ch2 ch6 ch7 Selection criteria are the same as those for ch4 trigger run. Trigger efficiency is collected. Normalized to the number of selected events. MF~(2400-960)/(2400+960)~43% G4 prediction: 47% Small difference between ch1/ch7, ch2/ch6, and ch3/ch5. (Misalignment? Error in trigger inefficiency?) Geant4

15. ArgonneResult_2004-02-07.ppt15 83.5 keV Coincidence Trigger Run ch1 ch3 ch5ch2 ch6 ch7 MF~(2360-970)/(2360+970)~42% G4 prediction: 47.5% Small difference between ch1/ch7, ch2/ch6, and ch3/ch5. Selection criteria are the same as those in the previous page. Trigger efficiency is collected. Normalized to the number of selected events. Geant4

16. ArgonneResult_2004-02-07.ppt16 60.2 keV Coincidence Trigger Run ch1 ch3 ch5 ch2 ch6 ch7 MF~(2360-980)/(2360+980)~41% G4 prediction: 46% Difference between ch1/ch7, ch2/ch6 and ch3/ch5. Somewhat larger than those seen in 73.2keV/83.5keV runs. Selection criteria are the same as those in the previous page. Trigger efficiency is collected. Normalized to the number of selected events. Geant4

17. ArgonneResult_2004-02-07.ppt17 Summary To examine the performance of PoGO and verify the Geant4-based simulator, we conducted the beam test at Argonne National Laboratory. Meanwhile, we compared Geant4 and EGS4 polarized Compton scattering and found the difference. With a help of Y. Fukazawa at Hiroshima Univ., we fixed Geant4 and used it to simulate the Argonne beam test. (there is still ~10% difference between Geant4 and EGS4, and a further study is required). We obtained clear modulation with a PoGO prototype. Observed modulation factor was ~43%, and that predicted by Geant4 (with PoGO-fix) was ~47%. We succeeded in reproducing data with simulation in ~10%. The remaining difference could be explained by an unpolarized component of the beam and/or misalignment of scintillators.