1. 1 Triplet polarimeter M. Dugger, March 2015

2. M. Dugger, February 2012 2 Triplet production Pair production off a nucleon: γ nucleon → nucleon e + e -. For polarized photons σ = σ 0 [1 + PΣ cos(2φ)], where σ 0 is the unpolarized cross section, P is the photon beam polarization and Σ is the beam asymmetry Triplet production off an electron: γ e - → e R - e + e -, where e R represents the recoil electron Any residual momentum in the azimuthal direction of the e - e + pair is compensated for by the slow moving recoil electron. This means that the recoil electron is moving perpendicular to the plane containing the produced pair and can attain large polar angles.

3. 3 Event generator Diagrams used Screening correction Most important diagrams

4. 4 Triplet production (pair like) Here we have two electrons in final state and must include diagrams that have 4 ↔ 5 interchange 1 2 345 q Q 1 2 435 q Q 1 2 354 q Q 1 2 534 q Q time

5. 5 Triplet production (Compton like) Includes 4 ↔ 5 exchange 1 2 4Q q 5 3 1 2 4Q 53 1 2 5Q q 4 3 1 2 5Q 43 time

6. M. Dugger, February 2014 6 Screening correction

7. 7 Leonard Maximon informed me that the screening correction for triplet production should not be important for the beam asymmetry but was very important for the cross section Used the screening correction provided in the paper by Maximon and Gimm [1] to compare cross section results of the event generator to values from the NIST [1] L. C. Maximon, H. A. Gimm Phys. Rev. A. 23, 1, (1981).

8. 8 Comparison plot of total cross section for triplet production Black line: Total cross section from NIST Blue points: Total cross section from event generator without screening correction Red points: Total cross section from event generator with screening corrections included Very nice agreement once screening is included

9. 9 Most important diagrams The Mork paper [2] says that the Compton-like diagrams and the switched electron leg diagrams should be negligible at high photon energy [2] K. J. Mork Phys. Rev. 160, 5, (1967).

10. 10 Calculations Ran 100,000 events at E γ = 9.0 GeV using: Full calculation: σ = 10.856 mb Reduced calculation: σ = 10.855 mb Reduced calculation neglects Compton-like and crossed electron- line diagrams Reduced calculations are well within 0.1% of full calculations 1 2 345 q Q 1 2 435 q Q time

11. M. Dugger, February 2012 11 Comparison of GEANT4 study of triplet polarimeter to previous study The SAL detector δ-rays Pair to triplet ratio ASU simulation of SAL Could SAL have been modified to work in the Hall-D environment?

12. M. Dugger, February 2012 12 The GW SAL detector E γ = 220 to 330 MeV 2 mm scintillator converter Polarimeter located ~39 cm downstream of converter Recoil θ = 15 to 35 degrees Recoil φ = 0, 90, 180, 270 degrees with Δφ = 44 degrees Analyzing power at the event generator level = 12% Analyzing power from simulation 3-4% (post experiment) Measured analyzing power = 2.7% Quick check - Can ASU reproduce the GW results?

13. M. Dugger, February 2012 13 δ-ray comparison with Iwata 1993 simulation E δ is δ-ray kinetic energy after traveling through 1 mm of scintillator using Iwata’s polar geometry and scintillator widths BLUE: Current ASU GEANT4 results RED: Iwata GEANT3 (scaled to GEANT4 results by ratio of signal integration) Shapes of the distributions look similar E δ (MeV) ASU simulation E γ = 300 MeV Iwata simulation E γ = 250, 365, 450 MeV Note: ASU simulation did not wrap scintillators

14. M. Dugger, February 2012 14 NIST cross sections for triplet and pair production off carbon σ pair /σ triplet : 5.75 @ 300 MeV 5.16 @ 9.0 GeV Ratio does not vary much over large energy range

15. M. Dugger, February 2012 15 Comparison of ASU MC of SAL detector to GW results Note: ASU results are for E γ = 300 MeV and GW is of E γ = 220 to 330 MeV Analyzing power: At event generator level: 12.6 ± 0.1 % ASU; ~12% GW (no error reported) ASU simulation: 2.65 ± 0.05% ASU simulation (30 μm Al wrapped scintillators): 2.8 ± 0.1 % GW experiment: 2.7% (no error reported) GW simulation: 3-4% (range given with no error reported) ASU results are in agreement with the GW results for the SAL detector ☺

16. M. Dugger, February 2012 16 How could the SAL detector be modified to work in Hall-D environment?

17. M. Dugger, February 2012 17 Dependence of analyzing power on ΔE pair for 16 sector detector Same parameters as previous best configuration but now with 16 sectors instead of 4 paddle SAL design Analyzing power fairly constant for ΔE pair < 1750 MeV The 16 sector design increases the analyzing power to 19.1 ± 0.7 % from 17.5 ± 0.3 % of the 4 paddle design (ΔE pair < 1500 MeV) ΔE pair (MeV) Analyzing power (%)

18. M. Dugger, February 2012 18 Recap of modifications that would make SAL type detector work in Hall-D

19. 19 Detector Decided to use Micron S3 design instead of the S2 The S3 has 32 azimuthal sectors instead of 16 for the S2 22 mm 70 mm 1 mm thick

20. 20 Preliminary design (slide 1) Micron S3 Converter 200 events thrown

21. 21 Micron S3 Converter Mounting plate and brackets Having a removable plate will allow for easy modification of how the detector is mounted without having to modify the chamber Preliminary design (slide 2)

22. 22 Micron S3 Converter Mounting plate and brackets Chamber with electrical feed- through flange, and blank flange Inner dimensions: 11in by 9in by 9in Preliminary design (slide 3) Actual design: 12 in by 12 in by 12 in

23. 23 Includes ribbon cable from detector to electrical feed- through Preliminary design (slide 4)

24. 24 With front door in see through mode 200 events thrown Preliminary design (slide 5)

25. 25 Simulation φ (degrees) Energy deposited (MeV) Generated pairs and triplets with E γ = 9 GeV Required energy of e + e - pair to be within 1.75 GeV of each other Required energy deposition in detector to be greater than 200 keV Converter: 35 μm beryllium Used full calculation (all diagrams included)

26. 26 Simulation results cross section weighted counts φ (degrees) Assumed collimated photon rate in coherent peak : 99 MHz Δt = 4 hours Analyzing power: 0.186 Polarization uncertainty: 0.01 Rates: Total rate on device = 955 Hz Rate surviving software and trigger cuts = 64 Hz where N ≡ Rate surviving cuts * 4 hour, P ≡ Polarization = 0.4, and α ≡ analyzing power Assumed

27. Polarimeter location (red box) 27 Future home Sources of magnetic fields in red circles

28. 28 B-field study Study performed in April 2012 Applied magnetic field in vertical direction

29. M. Dugger, April 2012 29 Effect of B-field on δ-rays x (cm) y (cm) No field → 350 gauss field →

30. 30 Azimuthal distribution with applied B-field φ 350 gauss field applied A[1+Bcos(2φ)] A[1+Bcos(2φ)+Ccos(φ)]

31. 31 Analyzing power vs. B-field Analyzing power (B) Field strength (gauss) Small field → Small systematic effect

32. 32 Polarimeter stand in collimator cave

33. 33 Upstream of polarimeter stand Secondary collimator Secondary sweep magnet Polarimeter stand

34. 34 Further upstream of polarimeter stand Primary sweep magnet Secondary collimator

35. 35 Construction

36. 36 Vacuum system When the polarimeter is installed in the collimator cave, the vacuum will come from the beam line In the test bench, the vacuum has to be provided by a temporary system Using a rotary vane pump for the vacuum system of the test bench Rotary vane pumps will back-stream oil and this issue must be addressed

37. 37 VisiTrap VisiTrap will catch any back- streaming before it hits the vacuum hose

38. 38 Molecular Sieve and Stinger Molecular sieve will catch stray contaminates Loaded sieve with zeolite and heated for two hours

39. 39 Vacuum system attached to chamber (view 1) Cleaned chamber with: Acetone Methonal DI water Attached the vacuum system

40. 40 Leakage and outgassing tests Procedure: Pump down chamber Close butterfly valve between vacuum system and chamber Record the pressure as a function of time cycle 1 Slope = 0.0266 mTorr/min

41. 41 Vacuum leakage test results (empty chamber) For area and volume calculations of the chamber I included all of the flanges Volume ~ 29.5 liters. Surface area ~ 6500 cm 2 Outgassing rate = (Volume/Area)*dP/dt Tim Whitlatch said steel will outgas at a rate of 2E-09 Torr*l/(cc*s) It looks like the test is consistent with the dP/dt of the chamber being from the outgassing of steel: No big obvious leaks

42. 42 Five hour pump down to ~20 mTorr Q l = V*dp/dt found to be 1.80x10 -4 Torr*liter/s A turbo pump on the chamber with a flow rate of 100 liters/s with a working pressure of 2x10 -5 Torr will have a Q w = 2x10 -3 Torr*liter/s Pfeiffer vacuum says that a system is adequately tight if Q w > 10*Q l Putting a turbo pump with flow rate 100 liters/s on the base of the chamber should be sufficient to maintain a vacuum of 2x10 -5 Torr Vacuum test results (detector in chamber)

43. 43 Detector upstream view with source stand and Po210 source Teflon fasteners connect detector to supports

44. 44 Detector downstream view

45. 45 Preamps Decided to have a parallel development of the preamps: Glasgow is building a pre-amplification system based off of the Rutherford Appleton Laboratory RAL-108 pramps and custom motherboards ASU is using a pre-amplification system from Swan research (“Box16 preamps”)

46. 46 Swan preamps The STARS detector uses Micron S2 with swan research preamps Input view Output view 16 channel box Preamp hybrid Stars detector

47. 47 Preamp to feedthrough cable assembly The Micron S3 detector uses special ribbon cable connectors Could not find suitable ribbon cables. Instead used Kapton wires that were individually placed in the cable connector 40 Wires attached to connector in picture shown

48. 48 Detector, cable and source

49. 49 Ring side cable Only enough preamps to instrument the sectors but made the ring side cables first

50. 50 Preamps wired up and ground connections Sector side cables Ring side set to ground

51. 51 Distribution box connected to preamp enclosure Original distribution box

52. 52 New distribution box (view 1) While Kei was at ASU getting trained to be a polarimeter expert he was able to help assemble to new distribution box Signal plate

53. 53 New distribution box (view 2) Power plate

54. 54 Copper preamp-box grounding (slide 1) Preamp supports made out of anodized aluminum Decided to help ground the preamp boxes by using copper foil on the preamp supports

55. 55 Copper preamp-box grounding (slide 2) Lined three sides of the preamp enclosure with the copper foil View: looking into the preamp enclosure through the opening for the vacuum chamber feedthrough flange Ground connector to ring side of detector

56. 56 Copper preamp-box grounding (slide 3) View: looking into the preamp enclosure from the top Can see the EM- shielding copper mesh for the fan inlet/outlet grounded to the copper foil

57. 57 Signal plate grounding Cutting copper foil for the signal plate grounding Also grounded to the input voltages (power plate)

58. 58 Signal plate and power plate grounding

59. 59 Fan leads Routed the fan leads through the preamp enclosure towards the distribution box

60. 60 View of polarimeter with original distribution box completely removed

61. 61 Wrapping signal wire around toroidal core reduces noise Putting AC Power Entry Module (with inline filter and earth-line choke) into LV supply also helped with the noise Noise reduction

62. 62 The silicon detector The detector is very much like a diode operated in reverse bias mode As the voltage is increased across the detector, the depletion region gets larger The larger the depletion region, the smaller the capacitance of the detector For each 3.6 eV of energy deposited in the depletion region there is one electron-hole pair that is created and then swept out of the detector

63. 63 Noise of preamps versus input capacitance Preamp noise has a linear relationship with the detector capacitance Typical noise versus detector capacitance plot

64. 64 High voltage Tennelec TC 952 For the test bench we are using a temporary power supply that is rather old The permanent power supply will be provided by JLab and will be of higher quality The temporary power supply has a ripple of about +/- 5 mV at 60 Hz

65. 65 Ripple and other noise as function of HV (slide 1) HV = 0VHV = 20V HV = 40V HV = 60V 10 mV/div 10 ms/div Using Po210 source

66. 66 Ripple and other noise as function of HV (slide 2) HV = 80VHV = 100V HV = 120V HV = 140V 10 mV/div 10 ms/div

67. 67 Ripple and other noise as function of HV (slide 3) HV = 160VHV = 180V HV = 200V 200 mV/div & 1 µs/div 10 mV/div 10 ms/div α

68. 68 Alpha o-scope picture Polonium 210 source Alpha energy = 5.3 MeV Signal about 500 mV

69. 69 Electron o-scope picture Cesium 137 source Signal about 25 mV for this shot Finer time scale for this shot (50 ns/div)

70. 70 Data acquisition system at ASU Using a Tektronix logging oscilloscope as a slow ADC Acquisition rate ~ 1 Hz  LabView signal express GUI

71. 71 Fit to signal Assume voltage has same form V = [Γ r V m /(Γ r - Γ f )][exp(Γ r t) – exp(Γ r t)] Voltage time (μs) Po210 signal

72. 72 Calibration (sector 3) Counts mV Center = 505.5 mV Po210 alpha source E k = 5304.33 keV One hour of data Calculated sensitivity = 95mV/MeV

73. 73 Alpha-test widths Looked at all 32 sectors Looks good except for a single channel (sector 32, lower preamp-box channel 10)

74. 74 Typical fit to signal for Ba133 source Voltage time (μs)

75. 75 MCData MC Generated photon energies: 223, 276, 302, 356, 383 keV Smeared energy deposited by standard deviation of 12 keV Fit: Centers locked to same photon energies that were generated in MC Standard deviation was the same for each Gaussian and allowed to vary Standard deviation from fit found to be 11+/- 1 keV Therefore, resolution of detector plus electronics is about 12 keV for this sector Ba133 MC compared to data (sector 3)

76. 76 Pile-up study 2.1% of total Threw 10 million photon events Only 469 events seen on detector Assume 10 8 Hz in photon range between 8.4 and 9 GeV Timing window of preamp pulse to be 18 μs For a single sector we expect 0.7% of events to have more than one signal in the timing window Pile-up should not be much of an issue

77. 77 Work still to be done at ASU Need to complete the positioning system (should be able to finish this week)

78. 78 Convertor tray Bottom of converter tray Top of converter tray

79. 79 Positioning system Still need to clean parts and install limit switches I expect the positioning system to be ready to ship by the end of this week

80. 80 Chamber crated up

81. 81 Initial work to be done at JLab Set up the chamber with vacuum system attached and do leakage and outgassing tests Attach the preamps and make sure that the signals look as they did at ASU Send the signals through the fADC and take data Attach the position control system and test New stuff

82. 82 Chamber Chamber at JLab JLab started receiving the polarimeter parts last week Initial test bench in the Experimental Equipment Laboratory (EEL) at Jefferson Lab