Polarized Electrons for Polarized Positrons PEPPo Jlab Injector

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 (i) (iii) (iv) (v) User Group Workshop and Annual Meeting, Newport News Motivations Experimental setup Commissioning Asymmetry measurements Preliminary results 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 C 3 q (P) • International Linear Collider • Elec(Posi)tron-ion Collider (LHe. C, e-RHIC, EIC, MEIC, ENC) • Thermal positron facility Newport News, June 2 -4, 2014 2/25

Motivations Eric Voutier Polarized Bremsstrahlung E. G. Bessonov, A. A. Mikhailichenko, EPAC (1996) A. P. Potylitsin, NIM A 398 (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 m. A 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

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 Newport News, June 2 -4, 2014 PAIR CREATION 4/25

Experimental setup Eric Voutier Principle of Operation Polarized Electrons (< 10 Me. V/c) strike production target Ee = 6. 3 Me. V Ie = 1 µA T 1 = 1 mm W S 1 Pee- Geant 4 Positron Transverse and Momentum Phase Space Selection T 1 D PEPPo PAIR PRODUCTION COMPTON TRANSMISSION BREMSSTRAHLUNG - pairs g produce and Polarized ee++econvert into polarized. Pgg Longitudinal e- (P produce e-) transfer into longitudinal (Pe+) circular and through transverse (Pg)elliptical whose transmission g whose (Pg) a polarization averages zero polarized iron is target (PT) to depends component proportional to Pe-on Pg. PT J. Dumas, Ph. D Thesis (2011) PT S 2 Pe+ D e+ Calorimeter T 2 Compton Transmission Polarimeter PEPPo measured the longitudinal polarization transfer in the 3. 07 -6. 25 Me. V/c momentum range. Newport News, June 2 -4, 2014 5/25

Experimental setup Eric Voutier Experiment Layout Ø 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 p. A – 1 µA Energy measurement d. E/E<0. 5% Polarization measurement d. P/P<3% Laser PEPPo Variable energy 3. 1 -8. 2 Me. V/c Polarization controls 30 Hz fast heilicity reversal (delayed) Slow laser polarization reversal (half-wave plate) 4 p spin rotator Newport News, June 2 -4, 2014 6/25

Experimental setup Eric Voutier Viewers Beam position monitors Solenoid ELEGANT beam optics Viewers Polarized Analyzing Target (7. 5 cm Fe) Solenoid Dipoles Corrector magnets PEPPo branch jonction Quadrupoles Faraday Cup Production Target G 4 PEPPo experiment model T 1 (0. 1 -1 mm W) Annihilation detector Viewer Positron Selection Device Corrector magnets Reconversion Target T 2 (2 mm W) Compton Transmission Polarimeter Newport News, June 2 -4, 2014 7/25

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

Commissioning Eric Voutier Cavity gradient calibration Spectrometer current calibration SRF cavity gradient (MV/m) Spectrometer current (A) S 1 current optimization at 5. 5 Me. V/c Current @ T 2 (arbitrary) Electron beam momentum (Me. V/c ) Momentum Calibration S 1 current (A) Ø The spectrometer current/momentum was calibrated with the electron beam. Ø The collection and transport solenoid currents were optimized with degraded electrons, and confirmed with produced positrons. Newport News, June 2 -4, 2014 9/25

Commissioning Eric Voutier Positron Signal Ø Two Na. I detectors were used to measure the back-to-back photons emitted by the annihilation of positrons in an insertable target. Target IN Target OUT Na 22 4 Me. V/c e+ collected from 0. 5 n. A 7 Me. V/c e- on 1 mm W target Newport News, June 2 -4, 2014 10/25

Commissioning Eric Voutier Analyzing Magnet Response Ø 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

Commissioning Eric Voutier Polarization Sensitivity Orientation 4 p spin rotator determines e- polarization orientation. helicit Rev polarity Newport News, June 2 -4, 2014 magnet PT = 7. 53% ± 0. 04%Stat. ± 0. 06%Syst. (0, Pe-, 0) eam erse b Reverse Pe- = 83. 7% ± 2. 8%Stat. ± 0. 6%Syst. (Pe-, 0, 0) y (0, 0, Pe-) 12/25

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

Asymmetry measurements Eric Voutier DAQ Components Ø Cs. I crystals a (6× 6× 28 cm 3) are coupled to PMTs equiped with LPSC custom amplified basis to extend the PMT life-time in the high rate environment of PEPPo. Ø The ~2 µs long and 2 V optimized signal is fed into the JLab custom FADC 250 that sampled the signal at 250 MHz. Hamamatsu R 6236 -100 FADC 250 Newport News, June 2 -4, 2014 The flexibility of the FADC 250 allows for 3 data taking modes : - Sample (500 samples /detector event); - Semi-integrated (1 integral / detector event); - Integrated (1 integral /helicity gate event). 14/25

Asymmetry measurements Eric Voutier Integrated Mode Operation Ø 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). h- h+ E- E+ E+ Simulation Newport News, June 2 -4, 2014 h+ h- Helicity frequency = 30 Hz Helicity delay = 8 windows Helicity pattern = quartet (+--+ or -++-) E- 15/25

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. Ø Pe(Me. V/c) Mode Ie- @ T 2 3. 08 Int. 60 p. A 4. 02 Int. 23 p. A 5. 34 Int. 25 p. A 6. 25 Int. 10 p. A 7. 19 Int. 10 p. A Newport News, June 2 -4, 2014 A. Adeyemi 16/25

Asymmetry measurements Eric Voutier Charge Particle Trigger Vacuum window photon e+ Trigger Scintillator Reconversion Target C A L O R I M E T E R Ø The DAQ trigger for positron measurements constitutes of a coincidence between a thin scintillator placed prior the reconversion target, and the central crystal (PMT 5). Drastic reduction of the neutral background. Newport News, June 2 -4, 2014 17/25

Asymmetry measurements Eric Voutier Semi-Integrated Mode Operation Ø 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 -++-) Ø 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

Asymmetry measurements Eric Voutier Energy Deposition Spectra 511 ke. V from e+ annihilation at rest Time (au) e+ Data @ 6. 25 Me. V/c Bremsstrahlung end-point Energy (FADC units) Ø The location of the 511 ke. V 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

Asymmetry measurements Eric Voutier Positron Compton Asymmetries e+ Data @ 6. 25 Me. V/c o P P E P y r a n i Prelim Statistics only Newport News, June 2 -4, 2014 20/25

Asymmetry measurements Eric Voutier Positron Data Summary Ø PEPPo measured the longitudinal polarization transfer from 8. 19 Me. V/c e- to 3. 07 -6. 25 Me. V/c e+, and explored influence of the target thickness. Mom (Me. V/c) Mode Set Ie- @ T 1 Target (mm) 3. 07 Sem. 1 380 n. A 1 4. 02 Sem. 1 25 n. A 1 5. 54 Sem. 1 95 n. A 1 6. 25 Sem. 1 380 n. A 1 3. 07 Sem. 2 120 n. A 1 3. 07 Sem. 2 380 n. A 0. 1 4. 02 Sem. 2 130 n. A 1 5. 54 Sem. 2 200 n. A 1 6. 25 Sem. 2 620 n. A 1 ² Two data set featuring different shielding configurations. ² 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

Preliminary results Eric Voutier Electron Analyzing Power Ø There is a bug in the Ø The energy dependence of polarized transportion the PEPPo measurements of process starting at version the 9. 0. electron analyzing power, is consistent with Ø expectations. PEPPo is now using version 8. 3, modified to include Ø There existsphoto-electric a systematic polarized shift between GEANT 4 effect and bugs fixes 9. 6 or simulations and PEPPo data changes in the polarization ? package through version > 8. 3. Newport News, June 2 -4, 2014 R. Adeyemi Suleiman A. 23/25

Preliminary results Eric Voutier Positron Polarization Set 1 (Initial Run) Set 2 (Improved Shielding) Electron Beam Polarization o P P PE ry a n i m Preli Pe+ = AT / k Ae- PT Positron polarization deduced usingasymmetries measured electron beam andpositron target Ø Significant non-zeroisexperimental increasing with polarizations, electron analyzing power, experimental asymmetry, and momentum sign efficient polarization transfer from electrons to positrons. estimated e+/e- analyzing power ratio (1. 1 -1. 4). Newport News, June 2 -4, 2014 24/25

PEPPo Collaboration P. Aderley 1, A. Adeyemi 4, P. Aguilera 1, M. Ali 1, H. Areti 1, M. Baylac 2, J. Benesch 1, G. Bosson 2, B. Cade 1, A. Camsonne 1, L. Cardman 1, J. Clark 1, P. Cole 5, S. Covert 1, C. Cuevas 1, O. Dadoun 3, D. Dale 5, J. Dumas 1, 2, E. Fanchini 2, T. Forest 5, E. Forman 1, A. Freyberger 1, E. Froidefond 2, S. Golge 6, J. Grames 1, P. Guèye 4, J. Hansknecht 1, P. Harrell 1, J. Hoskins 8, C. Hyde 7, R. Kazimi 1, Y. Kim 1, 5, D. Machie 1, K. Mahoney 1, R. Mammei 1, M. Marton 2, J. Mc. Carter 9, M. Mc. Caughan 1, M. Mc. Hugh 10, D. Mc. Nulty 5, T. Michaelides 1, R. Michaels 1, C. Muñoz Camacho 11, J. -F. Muraz 2, K. Myers 12, A. Opper 10, M. Poelker 1, J. -S. Réal 2, L. Richardson 1, S. Setiniyazi 5, M. Stutzman 1, R. Suleiman 1, C. Tennant 1, C. -Y. Tsai 13, D. Turner 1, A. Variola 3, E. Voutier 2, Y. Wang 1, Y. Zhang 12 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 1 Many thanks for advice, equipment loan, GEANT 4 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

Polarimeter target polarization Eric Voutier Analyzing Magnet Characterization E. Froidefond et al. , IPAC 13, MOPWA 079 Ø The static modeling of the analyzing magnet developed within OPERA-2 D 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

Polarimeter target polarization Eric Voutier Magnetic Flux Measurement Ø The iron core target is equipped with 3 pick-up coils measuring the magnetic flux generated upon magnet current variation. Ø 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