Triplet polarimeter M. Dugger, March

Transcription

1 Triplet polarimeter M. Dugger, March

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. M. Dugger, February

3 Event generator Diagrams used Screening correction Most important diagrams 3

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

5 Triplet production (Compton like) time 4 Q q Q q Q Q Includes 4 5 exchange 1 2 5

6 Screening correction M. Dugger, February

7 Screening correction 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). 7

8 Comparison plot of total cross section for 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 triplet production Very nice agreement once screening is included 8

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). 9

10 3 4 5 Calculations time 1 q Q 1 q Q 2 2 Ran 100,000 events at E γ = 9.0 GeV using: Full calculation: σ = mb Reduced calculation: σ = mb Reduced calculation neglects Compton-like and crossed electronline diagrams Reduced calculations are well within 0.1% of full calculations 10

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? M. Dugger, February

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? M. Dugger, February

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 ASU simulation E γ = 300 MeV E δ (MeV) Iwata simulation E γ = 250, 365, 450 MeV Note: ASU simulation did not wrap scintillators M. Dugger, February

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

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 M. Dugger, February

16 How could the SAL detector be modified to work in Hall-D environment? Air Vacuum Converter rad length 10-4 E 9 GeV ΔE pair < 1.5 GeV Analyzing power 2.8(1) % X 6.9(1) % X X 12.5(2) % X X X 10.6(2) % X X X X 17.5(3) % M. Dugger, February

17 Analyzing power (%) 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) M. Dugger, February

18 Recap of modifications that would make SAL type detector work in Hall-D Air Vacuum Converter rad length 10-4 E 9 GeV ΔE pair < 1.5 GeV 16 Sector Analyzing power 2.8(1) % X 6.9(1) % X X 12.5(2) % X X X 10.6(2) % X X X X 17.5(3) % X X X X X 19.1(7) % M. Dugger, February

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

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

21 Preliminary design (slide 2) 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 21

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

23 Preliminary design (slide 4) Includes ribbon cable from detector to electrical feedthrough 23

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

25 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 Simulation Required energy deposition in detector to be greater than 200 kev Converter: 35 μm beryllium φ (degrees) Used full calculation (all diagrams included) 25

26 cross section weighted counts Simulation results Assumed collimated photon rate in coherent peak : 99 MHz Δt = 4 hours Analyzing power: Polarization uncertainty: 0.01 Assumed P P 1 N 2 P 2 2 where N Rate surviving cuts * 4 hour, P Polarization = 0.4, and α analyzing power 1 Rates: Total rate on device = 955 Hz Rate surviving software and trigger cuts = 64 Hz φ (degrees) 26

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

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

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

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

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

32 Polarimeter stand in collimator cave 32

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

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

35 Construction 35

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 36

37 VisiTrap VisiTrap will catch any backstreaming before it hits the vacuum hose 37

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

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

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 Slope = mtorr/min cycle 1 40

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) Cycle dp/dt (mtorr/min) dp/dt (Torr/s) V/A*dP/dt (Torr*l/cc*s) * 10^ E * 10^ E * 10^ E * 10^ E-10 It looks like the test is consistent with the dp/dt of the chamber being from the outgassing of steel: No big obvious leaks 41

42 Vacuum test results (detector in chamber) 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 42

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

44 Detector downstream view 44

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 ) 45

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

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 47

48 Detector, cable and source 48

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

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

51 Distribution box connected to preamp enclosure Original distribution box 51

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 52

53 New distribution box (view 2) Power plate 53

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 54

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 55

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

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

58 Signal plate and power plate grounding 58

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

60 View of polarimeter with original distribution box completely removed 60

61 Noise reduction 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 61

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 62

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

64 High voltage For the test bench we are using a temporary power supply that is rather old Tennelec TC 952 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 64

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

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

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

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

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

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

71 Voltage 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)] Po210 signal time (μs) 71

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

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

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

75 Ba133 MC compared to data (sector 3) MC Data 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 75

76 Pile-up study 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 2.1% of total 76

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

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

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 79

80 Chamber crated up 80

81 Crate counterbalance Undergraduate cratecounterbalance (Brianna) Brianna is also my machine-shop buddy and she helped build the polarimeter 81

82 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

83 Chamber at JLab JLab started receiving the polarimeter parts last week Chamber Initial test bench in the Experimental Equipment Laboratory (EEL) at Jefferson Lab 83

84 A polarimeter does not build itself It takes a village 84

85 ASU Meson Physics Group participation (listed in order of seniority) Barry Ritchie (group leader): Helped with concept, design and construction Michael Dugger (research prof): Concept, design, construction Kei Moriya (post-doc): Installation of polarimeter, integration of electronics with fadcs and is the polarimeter expert at JLab Ross Tucker (graduate student): Helped with noise reduction and design of initial distribution box Ben Prather (undergraduate): Worked on event generator Todd Hodges (undergraduate past member): Worked on event generator and GEANT4 simulations Brianna Thorpe (undergraduate): Worked on construction of polarimeter and Arduino development 85

86 Participation outside of ASU Richard Jones (Professor at UCON): Provided initial event generator and helped with concept and design Dennis Swan (Swan research): Built the preamps and helped in decisions regarding the particular configuration of the preamps we use Leonard Maximon (Professor at GW): Helped with event generator Ken Livingston (Glasgow): Helped with concept and design Alexander Somov (JLab): Helped with integration of polarimeter with pair spectrometer Tim Whitlatch and mechanical group (JLab): Helped with design and installation Fernando Barbosa (JLab): Helped with electronics and installation Hovanes Egiyan (JLab): Helped with design and provided slow controls David Lawrence (JLab and past ASU group member): Helped with DAQ Lubomir Pentchev (JLab): Helped with installation and fadcs Beni Zihlmann (JLab): Helped with installation and fadcs I have had a lot of help so far and have probably missed some people in the participation list 86