Polarized Electrons for Polarized Positrons PEPPo @ 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

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 2/25

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 3/25 XXVth International Workshop on Nuclear Theory

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) 055208 BREMSSTRAHLUNG PAIR CREATION Newport News, June 2-4, 2014 4/25 XXVth International Workshop on Nuclear Theory

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 3.07-6.25 MeV/c momentum range. Newport News, June 2-4, 2014 5/25 XXVth International Workshop on Nuclear Theory

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 3.1-8.2 MeV/c Newport News, June 2-4, 2014 6/25 XXVth International Workshop on Nuclear Theory

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 7/25 XXVth International Workshop on Nuclear Theory

Commissioning Eric Voutier Newport News, June 2-4, 2014 8/25

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) Current @ 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

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

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

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 12/25

Asymmetry Measurements Operation Electron Calibration Polarized positron measurements Newport News, June 2-4, 2014 13/25

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 R6236-100 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

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 15/25

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 Ie- @ 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

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

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

Energy Deposition Spectra Asymmetry measurements Eric Voutier Energy Deposition Spectra e+ Data @ 6.25 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

PEPPo Preliminary Positron Compton Asymmetries Asymmetry measurements Eric Voutier Positron Compton Asymmetries e+ Data @ 6.25 MeV/c PEPPo Preliminary Statistics only Newport News, June 2-4, 2014 20/25

Positron Data Summary Asymmetry measurements Eric Voutier Positron Data Summary PEPPo measured the longitudinal polarization transfer from 8.19 MeV/c e- to 3.07-6.25 MeV/c e+, and explored influence of the target thickness. Mom (MeV/c) Mode Set Ie- @ 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). 21/25

Preliminary Results Electron analyzing power Positron polarization Newport News, June 2-4, 2014 22/25

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 23/25

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 (1.1-1.4). Significant non-zero experimental asymmetries increasing with positron momentum sign efficient polarization transfer from electrons to positrons. Newport News, June 2-4, 2014 24/25

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 2 LPSC, Grenoble, France 3 LAL, Orsay, France 4 Hampton University, Hampton, VA, USA 5 Idaho State University & IAC, Pocatello, ID, USA 6 North Carolina University, Durham, NC, USA 7 Old Dominion University, Norfolk, VA, US 8 The College of William & Mary, Williamsburg, VA, USA 9 University of Virginia, Charlottesville, VA, USA 10 George Washington University, Washington, DC, USA 11 IPN, Orsay, France 12 Rutgers University, Piscataway, NJ, USA 13 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 25/25

Eric Voutier XXVth International Workshop on Nuclear Theory

±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

< 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