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P olarize d E lectrons f or P olarized Po sitrons 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

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slide1

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

slide2

Physics Motivations

  • Electromagneticformfactors (U,P)
  • Generalized parton distributions (U,P)
  • Inclusive structure functions (U,P)
  • Search for the U-boson of darkmatter (U)
  • Charge conjugation violation to access C3q (P)
  • International LinearCollider
  • Elec(Posi)tron-ion Collider (LHeC, e-RHIC, EIC, MEIC, ENC)
  • Thermal positron facility

2/25

Newport News, June 2-4, 2014

slide3

e-→g→e+

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.

Sustainablepolarizedelectronintensities up to 4 mA have been demonstratedfrom a superlattice photocathode.

R. Suleiman et al., PAC’11, New York (NJ, USA), March 28 – April 1, 2011

3/25

Newport News, June 2-4, 2014

slide4

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

PAIR CREATION

BREMSSTRAHLUNG

4/25

Newport News, June 2-4, 2014

slide5

Experimental setup

Eric Voutier

Geant4

Principle of Operation

Polarized Electrons

(< 10 MeV/c) strike production target

Positron Transverse and Momentum PhaseSpace Selection

Ee = 6.3 MeV

Ie= 1 µA

T1 = 1 mm W

S1

Pe-

PEPPo

D

e-

T1

PAIR PRODUCTION

g produce e+e- pairs and transfer Pg into longitudinal (Pe+) and transverse polarization averages to zero

  • BREMSSTRAHLUNG
  • Longitudinal e- (Pe-) produce elliptical g whose circular (Pg) component is proportional to Pe-

J. Dumas, PhD Thesis (2011)

COMPTON TRANSMISSION

Polarized e+ convert into polarized g (Pg) whose transmission through a polarized iron target (PT) depends on Pg.PT

Pe+

S2

PT

D

Calorimeter

e+

T2

Compton Transmission Polarimeter

PEPPomeasured the longitudinal polarization transfer

in the 3.07-6.25 MeV/cmomentum range.

5/25

Newport News, June 2-4, 2014

slide6

Energy measurement

dE/E<0.5%

Intensity controls

10 pA – 1 µA

Polarization measurement

dP/P<3%

PEPPo

Variable energy

3.1-8.2 MeV/c

Polarization controls

30 Hz fast heilicity reversal (delayed)

Slow laser polarization reversal (half-wave plate)

4p spin rotator

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 polarizedelectron beamentering the PEPPo apparatus.

Laser

6/25

Newport News, June 2-4, 2014

slide7

Viewers

Beam position monitors

Solenoid

ELEGANT beam optics

Viewers

Polarized Analyzing Target

(7.5 cm Fe)

Solenoid

Dipoles

Corrector magnets

Quadrupoles

PEPPo branch

jonction

Faraday Cup

Production Target

T1 (0.1-1 mm W)

Annihilation detector

Viewer

Positron Selection Device

Corrector magnets

ReconversionTarget

T2 (2 mm W)

Compton Transmission Polarimeter

Experimental setup

Eric Voutier

G4PEPPo experiment model

7/25

Newport News, June 2-4, 2014

slide8

Commissioning

Eric Voutier

8/25

Newport News, June 2-4, 2014

slide9

Commissioning

Eric Voutier

Momentum Calibration

S1currentoptimizationat 5.5 MeV/c

Cavity gradient calibration

Spectrometercurrent calibration

Electron beammomentum (MeV/c)

Current @ T2 (arbitrary)

SRF cavity gradient (MV/m)

Spectrometercurrent (A)

S1 current (A)

  • The spectrometercurrent/momentumwascalibratedwith the electronbeam.
  • The collection and transport solenoidcurrentswereoptimizedwithdegradedelectrons, and confirmedwithproducedpositrons.

9/25

Newport News, June 2-4, 2014

slide10

Na22

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.

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

10/25

Newport News, June 2-4, 2014

slide11

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

11/25

Newport News, June 2-4, 2014

slide12

Commissioning

Eric Voutier

Polarization Sensitivity Orientation

4p spin rotator determines

e- polarization orientation.

(Pe-, 0, 0)

(0, 0, Pe-)

(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.

12/25

Newport News, June 2-4, 2014

slide13

AsymmetryMeasurements

  • Operation
  • Electron Calibration
  • Polarized positron measurements

13/25

Newport News, June 2-4, 2014

slide14

Asymmetrymeasurements

Eric Voutier

DAQ Components

  • CsIcrystalsa (6×6×28 cm3) are coupled to PMTsequipedwith LPSC custom amplified basis to extend the PMT life-time in the high rate environment of PEPPo.
  • The ~2 µs long and 2 Voptimized signal isfedinto the JLab custom FADC250 thatsampled the signal at250 MHz.

Hamamatsu R6236-100

  • The flexibility of the FADC250 allows for 3 data taking modes :
  • Sample (500samples /detector event);
  • Semi-integrated (1 integral / detector event);
  • Integrated (1 integral /helicity gate event).

FADC 250

14/25

Newport News, June 2-4, 2014

slide15

Asymmetrymeasurements

Eric Voutier

Integrated Mode Operation

  • The integrated modeoperates for high rate conditions by integration of the PMT signal over the duration of an helicitygate(PEPPofirmwaredevoped by JLab).
  • Helicityfrequency = 30 Hz
  • Helicitydelay = 8 windows
  • Helicity pattern = quartet (+--+ or -++-)

h- h+ h+ h-

E- E+ E+ E-

Simulation

15/25

Newport News, June 2-4, 2014

slide16

Asymmetrymeasurements

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.

A. Adeyemi

16/25

Newport News, June 2-4, 2014

slide17

Asymmetrymeasurements

Eric Voutier

Charge Particle Trigger

Vacuum

window

Reconversion

Target

photon

C

A

L

O

R

I

M

E

T

E

R

e+

Trigger

Scintillator

  • The DAQ trigger for positron measurementsconstitutes of a coincidencebetween a thinscintillatorplacedprior the reconversion target, and the central crystal(PMT5).
  • Drasticreduction of the neutral background.

17/25

Newport News, June 2-4, 2014

slide18

Asymmetrymeasurements

Eric Voutier

Semi-Integrated Mode Operation

  • For eachcoincidence trigger, the PMT signals are registered in the form of one single valuecorresponding to the signal integrated over 2 µs, and istagged by the helicitystatus of the electronbeam.

Simulation

Helicityfrequency = 30 Hz

Helicitydelay = 0,8 windows

Helicity pattern = quartet (+--+ or -++-)

  • Experimentalasymmetryisdetermined for eachenergy bin and a correspondingpositron polarizationisdeterminedknowingfromcalibrated simulations the energydependence of the positron analyzing power.

18/25

Newport News, June 2-4, 2014

slide19

Asymmetrymeasurements

Eric Voutier

Energy Deposition Spectra

e+ Data @ 6.25 MeV/c

511 keVfrom e+ annihilation atrest

Time (au)

Bremsstrahlung

end-point

Energy (FADC units)

Energy (FADC units)

  • The location of the 511 keVpeakisused 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 energymeasurementis2.3%.

19/25

Newport News, June 2-4, 2014

slide20

Asymmetrymeasurements

Eric Voutier

Positron Compton Asymmetries

e+ Data @ 6.25 MeV/c

PEPPo Preliminary

Statisticsonly

20/25

Newport News, June 2-4, 2014

slide21

Asymmetrymeasurements

Eric Voutier

Positron Data Summary

  • PEPPomeasured the longitudinal polarizationtransferfrom8.19 MeV/ce- to 3.07-6.25 MeV/c e+, and explored influence of the targetthickness.
  • Two data setfeaturingdifferentshielding configurations.
  • Threedifferentanalysisschemes : energydependent, energyindependent (helicitygatedscaler), energyintegrated(link to electron calibration).

21/25

slide22

PreliminaryResults

  • Electron analyzing power
  • Positron polarization

22/25

Newport News, June 2-4, 2014

slide23

Preliminaryresults

Eric Voutier

Electron Analyzing Power

  • There is a bug in the polarizedtransportionprocessstartingatversion 9.0.
  • PEPPoisnowusing version 8.3, modified to includepolarizedphoto-electriceffect and bugs fixes or changes in the polarization packagethrough version > 8.3.
  • The energydependence of the PEPPomeasurements of the electronanalyzing power, isconsistentwithexpectations.
  • There exists a systematic shiftbetween GEANT4 9.6 simulations and PEPPo data ?

R. Suleiman

A. Adeyemi

23/25

Newport News, June 2-4, 2014

slide24

Preliminaryresults

Eric Voutier

Positron Polarization

Set 1 (Initial Run)

Set 2 (Improved Shielding)

Set 1 (Initial Run)

Set 2 (Improved Shielding)

Electron

Beam

Polarization

PEPPo Preliminary

Pe+ = AT / k Ae-Pe-PT

  • Positron polarizationisdeducedusingmeasuredelectronbeam and targetpolarizations, electronanalyzing power, experimentalasymmetry, and estimated e+/e-analyzing power ratio (1.1-1.4).
  • Significantnon-zeroexperimentalasymmetriesincreasingwith positron momentumsign efficient polarizationtransferfromelectrons to positrons.

24/25

Newport News, June 2-4, 2014

slide25

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

Manythanks for advice, equipmentloan, GEANT4 modeling support, and funding to

SLAC E-166 Collaboration

International LinearCollider Project

Jefferson Science Association Initiatives Award

25/25

Newport News, June 2-4, 2014

slide27

Polarimeter targetpolarization

Eric Voutier

Analyzing Magnet Characterization

E. Froidefond et al., IPAC13, MOPWA079

  • The static modelingof 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

slide28

Polarimeter targetpolarization

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