1. Polarized Electrons for Polarized Positrons
Jlab Injector
Eric Voutier on behalf of the PEPPo Collaboration
Laboratoire de Physique Subatomique et de Cosmologie
Grenoble, France
Motivations
Experimental setup
Commissioning
Asymmetry measurements
Preliminary results
User Group Workshop and Annual Meeting, Newport News
June 2-14, 2014

2. Physics Motivations Electromagnetic form factors (U,P)
Generalized parton distributions (U,P)
Inclusive structure functions (U,P)
Search for the U-boson of dark matter (U)
Charge conjugation violation to access C3q (P)
International Linear Collider
Elec(Posi)tron-ion Collider (LHeC, e-RHIC, EIC, MEIC, ENC)
Thermal positron facility
Newport News, June 2-4, 2014
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3. e- → g → e+ Polarized Bremsstrahlung Motivations
Eric Voutier
Motivations
Eric Voutier
Polarized Bremsstrahlung
E.G. Bessonov, A.A. Mikhailichenko, EPAC (1996) A.P. Potylitsin, NIM A398 (1997) 395
PEPPo has studied the feasibility of using bremsstrahlung from polarized electrons for the production of polarized positrons.
e- → g → e+
Sustainable polarized electron intensities up to 4 mA have been demonstrated from a superlattice photocathode.
R. Suleiman et al., PAC’11, New York (NJ, USA), March 28 – April 1, 2011
Newport News, June 2-4, 2014
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XXVth International Workshop on Nuclear Theory

4. Polarization Transfer in Bremsstrahlung and Pair Production
Eric Voutier
Motivations
Eric Voutier
Polarization Transfer in
Bremsstrahlung and Pair Production
H. Olsen, L. Maximon, PR 114 (1959) 887
E.A. Kuraev, Y.M. Bystritskiy, M. Shatnev, E. Tomasi-Gustafsson, PRC 81 (2010)
BREMSSTRAHLUNG
PAIR CREATION
Newport News, June 2-4, 2014
4/25
XXVth International Workshop on Nuclear Theory

5. Principle of Operation
Eric Voutier
Experimental setup
Eric Voutier
Principle of Operation S1 D S2
Pe+
Positron Transverse and Momentum Phase Space Selection e+
PAIR PRODUCTION
g produce e+e- pairs and transfer Pg into longitudinal (Pe+) and transverse polarization averages to zero
Ee = 6.3 MeV
Ie = 1 µA
T1 = 1 mm W
Geant4
PEPPo
J. Dumas, PhD Thesis (2011)
Pe- e- T1
Polarized Electrons
(< 10 MeV/c) strike production target
BREMSSTRAHLUNG
Longitudinal e- (Pe-) produce elliptical g whose circular (Pg) component is proportional to Pe-
COMPTON TRANSMISSION
Polarized e+ convert into polarized g (Pg) whose transmission through a polarized iron target (PT) depends on Pg.PT T2 PT
Calorimeter
Compton Transmission Polarimeter
PEPPo measured the longitudinal polarization transfer
in the MeV/c momentum range.
Newport News, June 2-4, 2014
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XXVth International Workshop on Nuclear Theory

6. Experiment Layout Experimental setup
Eric Voutier
Experimental setup
Eric Voutier
Experiment Layout
PEPPo ran at the CEBAF injector, taking advantage of the existing beam diagnostics that determine with precision the properties of the polarized electron beam entering the PEPPo apparatus.
Intensity controls
10 pA – 1 µA
Energy measurement
dE/E<0.5%
Polarization measurement
dP/P<3%
PEPPo
Laser
Polarization controls
30 Hz fast heilicity reversal (delayed)
Slow laser polarization reversal (half-wave plate)
4p spin rotator
Variable energy
MeV/c
Newport News, June 2-4, 2014
6/25
XXVth International Workshop on Nuclear Theory

7. Polarized Analyzing Target
Eric Voutier
Experimental setup
Eric Voutier
Beam position monitors
Viewers
Corrector magnets
Quadrupoles
Dipoles
Solenoid
ELEGANT beam optics
PEPPo branch
jonction
Faraday Cup
Annihilation detector
Viewers
Viewer
Positron Selection Device
Reconversion Target
T2 (2 mm W)
Polarized Analyzing Target
(7.5 cm Fe)
Compton Transmission Polarimeter
Production Target
T1 (0.1-1 mm W)
Corrector magnets
Solenoid
G4PEPPo experiment model
Newport News, June 2-4, 2014
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XXVth International Workshop on Nuclear Theory

8. Commissioning
Eric Voutier
Newport News, June 2-4, 2014
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9. Momentum Calibration Commissioning
Eric Voutier
Momentum Calibration
Cavity gradient calibration
Spectrometer current calibration
S1 current optimization at 5.5 MeV/c
Electron beam momentum (MeV/c)
T2 (arbitrary)
SRF cavity gradient (MV/m)
Spectrometer current (A)
S1 current (A)
The spectrometer current/momentum was calibrated with the electron beam.
The collection and transport solenoid currents were optimized with degraded electrons, and confirmed with produced positrons.
Newport News, June 2-4, 2014
9/25

10. Positron Signal Commissioning
Eric Voutier
Commissioning
Eric Voutier
Positron Signal
Two NaI detectors were used to measure the back-to-back photons emitted by the annihilation of positrons in an insertable target.
Na22
Target IN
Target IN
Target OUT
Target OUT
4 MeV/c e+ collected from 0.5 nA 7 MeV/c e- on 1 mm W target
Newport News, June 2-4, 2014
10/25
XXVth International Workshop on Nuclear Theory

11. Analyzing Magnet Response
Commissioning
Eric Voutier
Analyzing Magnet Response
Experimental asymmetries are measured with respect to beam helicity ; they are linearly proportional to the target polarization, itself proportional to the target magnetization.
IHWP inserted
A. Adeyemi
Newport News, June 2-4, 2014
11/25

12. Polarization Sensitivity Orientation
Commissioning
Eric Voutier
Polarization Sensitivity Orientation
4p spin rotator determines
e- polarization orientation.
(0, 0, Pe-)
(Pe-, 0, 0)
(0, Pe-, 0)
Reverse magnet polarity
Reverse beam helicity
Pe- = 83.7% ± 2.8%Stat. ± 0.6%Syst.
PT = 7.53% ± 0.04%Stat. ± 0.06%Syst.
Newport News, June 2-4, 2014
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13. Asymmetry Measurements
Operation
Electron Calibration
Polarized positron measurements
Newport News, June 2-4, 2014
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14. DAQ Components Asymmetry measurements
Eric Voutier
DAQ Components
CsI crystals a (6×6×28 cm3) are coupled to PMTs equiped with LPSC custom amplified basis to extend the PMT life-time in the high rate environment of PEPPo.
The ~2 µs long and 2 V optimized signal is fed into the JLab custom FADC250 that sampled the signal at 250 MHz.
Hamamatsu R
The flexibility of the FADC250 allows for 3 data taking modes :
Sample (500 samples /detector event);
Semi-integrated (1 integral / detector event);
Integrated (1 integral /helicity gate event).
FADC 250
Newport News, June 2-4, 2014
14/25

15. Integrated Mode Operation
Asymmetry measurements
Eric Voutier
Integrated Mode Operation
h h h h-
E E E E-
The integrated mode operates for high rate conditions by integration of the PMT signal over the duration of an helicity gate (PEPPo firmware devoped by JLab).
Helicity frequency = 30 Hz
Helicity delay = 8 windows
Helicity pattern = quartet (+--+ or -++-)
Simulation
Newport News, June 2-4, 2014
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16. Electron Compton Asymmetries
Asymmetry measurements
Eric Voutier
Electron Compton Asymmetries
Combining experimental asymmetries measured for each analyzing magnet polarity and each laser polarization orientation (IHWP) allows to cancel-out eventual false asymmetries and isolate physics asymmetries.
Pe-
(MeV/c)
Mode T2
3.08
Int.
60 pA
4.02
23 pA
5.34
25 pA
6.25
10 pA
7.19
A. Adeyemi
Newport News, June 2-4, 2014
16/25

17. Drastic reduction of the neutral background.
Asymmetry measurements
Eric Voutier
Charge Particle Trigger
Vacuum
window
Reconversion
Target
photon C A L O R I M E T e+
Trigger
Scintillator
The DAQ trigger for positron measurements constitutes of a coincidence between a thin scintillator placed prior the reconversion target, and the central crystal (PMT5).
Drastic reduction of the neutral background.
Newport News, June 2-4, 2014
17/25

18. Semi-Integrated Mode Operation
Asymmetry measurements
Eric Voutier
Semi-Integrated Mode Operation
For each coincidence trigger, the PMT signals are registered in the form of one single value corresponding to the signal integrated over 2 µs, and is tagged by the helicity status of the electron beam.
Simulation
Helicity frequency = 30 Hz
Helicity delay = 0,8 windows
Helicity pattern = quartet (+--+ or -++-)
Experimental asymmetry is determined for each energy bin and a corresponding positron polarization is determined knowing from calibrated simulations the energy dependence of the positron analyzing power.
Newport News, June 2-4, 2014
18/25

19. Energy Deposition Spectra
Asymmetry measurements
Eric Voutier
Energy Deposition Spectra
e MeV/c
511 keV from e+ annihilation at rest
Time (au)
Bremsstrahlung
end-point
Energy (FADC units)
Energy (FADC units)
The location of the 511 keV peak is used for in-situ monitoring of the effective gain of the read-out chain, and link to radioactive source calibration data.
The global accuracy of the photon energy measurement is 2.3%.
Newport News, June 2-4, 2014
19/25

20. PEPPo Preliminary Positron Compton Asymmetries Asymmetry measurements
Eric Voutier
Positron Compton Asymmetries
e MeV/c
PEPPo Preliminary
Statistics only
Newport News, June 2-4, 2014
20/25

21. Positron Data Summary Asymmetry measurements
Eric Voutier
Positron Data Summary
PEPPo measured the longitudinal polarization transfer from 8.19 MeV/c e- to MeV/c e+, and explored influence of the target thickness.
Mom
(MeV/c)
Mode
Set T1
Target (mm)
3.07
Sem. 1
380 nA
4.02
25 nA
5.54
95 nA
6.25 2
120 nA
0.1
130 nA
200 nA
620 nA
Two data set featuring different shielding configurations.
Three different analysis schemes : energy dependent, energy independent (helicity gated scaler), energy integrated (link to electron calibration).
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22. Preliminary Results Electron analyzing power Positron polarization
Newport News, June 2-4, 2014
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23. Electron Analyzing Power
Preliminary results
Eric Voutier
Electron Analyzing Power
There is a bug in the polarized transportion process starting at version 9.0.
PEPPo is now using version 8.3, modified to include polarized photo-electric effect and bugs fixes or changes in the polarization package through version > 8.3.
The energy dependence of the PEPPo measurements of the electron analyzing power, is consistent with expectations.
There exists a systematic shift between GEANT4 9.6 simulations and PEPPo data ?
A. Adeyemi
R. Suleiman
Newport News, June 2-4, 2014
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24. Positron Polarization
Preliminary results
Eric Voutier
Positron Polarization
Set 1 (Initial Run)
Set 2 (Improved Shielding)
Electron
Beam
Polarization
Pe+ = AT / k Ae- Pe- PT
Set 1 (Initial Run)
Set 2 (Improved Shielding)
PEPPo Preliminary
Positron polarization is deduced using measured electron beam and target polarizations, electron analyzing power, experimental asymmetry, and estimated e+/e- analyzing power ratio ( ).
Significant non-zero experimental asymmetries increasing with positron momentum sign efficient polarization transfer from electrons to positrons.
Newport News, June 2-4, 2014
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25. PEPPo Collaboration
P. Aderley1, A. Adeyemi4, P. Aguilera1, M. Ali1, H. Areti1, M. Baylac2, J. Benesch1,
G. Bosson2, B. Cade1, A. Camsonne1, L. Cardman1, J. Clark1, P. Cole5, S. Covert1,
C. Cuevas1, O. Dadoun3, D. Dale5, J. Dumas1,2, E. Fanchini2, T. Forest5, E. Forman1,
Freyberger1, E. Froidefond2, S. Golge6, J. Grames1, P. Guèye4, J. Hansknecht1,
P. Harrell1, J. Hoskins8, C. Hyde7, R. Kazimi1, Y. Kim1,5, D. Machie1, K. Mahoney1,
R. Mammei1, M. Marton2, J. McCarter9, M. McCaughan1, M. McHugh10, D. McNulty5, T. Michaelides1, R. Michaels1, C. Muñoz Camacho11, J.-F. Muraz2, K. Myers12,
Opper10, M. Poelker1, J.-S. Réal2, L. Richardson1, S. Setiniyazi5, M. Stutzman1,
R. Suleiman1, C. Tennant1, C.-Y. Tsai13, D. Turner1, A. Variola3, E. Voutier2, Y. Wang1, Y. Zhang12
1 Jefferson Lab, Newport News, VA, US LPSC, Grenoble, France LAL, Orsay, France
4 Hampton University, Hampton, VA, USA Idaho State University & IAC, Pocatello, ID, USA
6 North Carolina University, Durham, NC, USA Old Dominion University, Norfolk, VA, US
8 The College of William & Mary, Williamsburg, VA, USA University of Virginia, Charlottesville, VA, USA George Washington University, Washington, DC, USA IPN, Orsay, France
12 Rutgers University, Piscataway, NJ, USA Virginia Tech, Blacksburg, VA, USA
Many thanks for advice, equipment loan, GEANT4 modeling support, and funding to
SLAC E-166 Collaboration
International Linear Collider Project
Jefferson Science Association Initiatives Award
Newport News, June 2-4, 2014
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26. Eric Voutier
XXVth International Workshop on Nuclear Theory

27. ±60 A operational current.
Polarimeter target polarization
Eric Voutier
Analyzing Magnet Characterization
E. Froidefond et al., IPAC13, MOPWA079
The static modeling of the analyzing magnet developed within OPERA-2D is controlled by the measured magnetic map of the fringe field of the solenoid at
±60 A operational current.
Newport News, June 2-4, 2014

28. < PT > = 7.53% ± 0.04%Coil ± 0.06%Opera
Polarimeter target polarization
Eric Voutier
Magnetic Flux Measurement
The iron core target is equipped with 3 pick-up coils measuring the magnetic flux generated upon magnet current variation.
Specific cycling procedures are used during the experiment to monitor the target polarization.
< PT > = 7.53% ± 0.04%Coil ± 0.06%Opera
Newport News, June 2-4, 2014