peppo · 2016. 12. 28. · j. grames, e. voutier et al., jlab experiment e12-11-105, 2011 polarized...

PEPPo

A Universal Access to Polarized Positrons

PEPPo @ CEBAF-Injector.JLab

(i) Physics motivations (ii) The PEPPo experiment (iii) PEPPo measurements (iv) Outlook

Eric Voutier on behalf of the PEPPo Collaboration

Institut de Physique Nucléaire d’Orsay Orsay, France

Paphos, November 2rd-7th, 2015 XIth Conference on Electromagnetic Interactions with Nucleons and Nuclei

Physics Motivations

• Electromagnetic form factors (U,P) • Inclusive structure functions (U,P)

• Generalized parton distributions (U,P)

• Search for the U-boson coupling to dark matter (U,P) • Charge conjugation violation to access C3q (P)

• International Linear Collider (U,P)

• Positron-ion and circular Colliders (LHeC, EIC, MEIC)

• Thermal positron facility (U,P)

Paphos, November 1st-7th, 2015

Hadronic Physics

Standard Model Tests

High Energy Physics

Applications

Two Photon Physics

Ø Following the very first measurements of polarization transfer observables in electron elastic scattering, the validity of the 1g exchange

approximation of the electromagnetic interaction has been questioned.

P.A.M. Guichon, M. Vanderhaeghen, PRL 91 (2003) 142303

3/17

Electromagnetic form factors

ε),Q(F~δeF~ε),Q(G~δe)Q(GG~ε),Q(G~δe)Q(GG~

23l3

2El

2EE

2Ml

2MM

=

+=

+=

Within the 2g exchange hypothesis, the electromagnetic structure of the nucleon may be parametrized by 3 generalized form factors, corresponding to 8 unknow quantities.

Eric Voutier


Electromagnetic form factors

Experimental Observables

M.P. Rekalo, E. Tomasi Gustafsson, NPA 742 (2004) 322 C. Carlson, M. Vanderhaeghen, ARNPS 57 (2007) 171

( )[ ] ( )[ ]313022 ~,~2~,~2 FGfGFGfGGG EEMMEMR dd

tedd

tes Â±Â±+=

( ) [ ] ( )[ ]( )31~,~~12 FGfGGGGGP EMMEMEtR ddd

tees Â±Â±

--=

( )[ ]( )3222 ~,~21 FGfGGP MMMlR ddes Â±-=

Combining polarized electrons and positrons allows a model independent separation of the electromagnetic form factors of the nucleon.

Ø Unpolarized e± elastic scattering and polarization transfert observables off the nucleon involve up to 5 unknown quantities.

5 unknown contributions for 6 independent observables

Cross Section

Polarization Transfert

4/17

Eric Voutier


N(e,e′gN) Differential Cross Section

M. Diehl at the CLAS12 European Workshop, Genova, February 25-28, 2009

( )INTlINTlDVCSlDVCSBHeP0 σ~Pσeσ~Pσσσ ++++=

Polarized electrons and positrons allow to separate the unknown amplitudes of the cross section for electro-production of photons.

INTDVCSBH00 σσσσ -+=-

INTDVCS00 σ~2σ~2σσ -=- --

-+

INT0000 σ2σσ =- -+

[ ] [ ] [ ] [ ] INT00000000 σ~4σσσσσσσσ =---=--- --

+-

-+

++

--

-+

+-

++

Electron observables

Electron & positron observables

Generalized parton distributions

( ) ( )[ ]INTlINTlDVCSlDVCSBHleP0

ePS σPσ~eσPσ~σPSσσ D+D+D+D+D+=

INTDVCS00 σ~2σ~2σσ D±D=- ±-

±+

Additional observables

[ ] [ ] INTDVCSBH σ4σ4σ4σσσσ D±D+D=--- ±--

±+-

±-+

±++

Eric Voutier

5/17 Paphos, November 1st-7th, 2015

PEPPo Experiment

• Polarized positron production • Proof-of-principle experiment

• Electron & positron polarimetry


E.G. Bessonov, A.A. Mikhailichenko, EPAC (1996) A.P. Potylitsin, NIM A398 (1997) 395

e- → g → e+

J. Grames, E. Voutier et al., JLab Experiment E12-11-105, 2011

Polarized Bremsstrahlung

Eric Voutier Polarized positron production

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

The purpose of the PEPPo (Polarized Electrons for Polarized Positrons) experiment at the CEBAF injector was to demonstrate feasibility

of using bremsstrahlung radiation of polarized electrons for the production of polarized positrons.


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

PAIR PRODUCTION

In the same target, g produce e+e- pairs and transfer Pg into longitudinal

(Pe+) and transverse polarization averages to zero

Pe-

e- T1

Polarized Electrons (< 10 MeV/c) strike production target


S1

D

D

S2 Pe+

Positron Transverse and Momentum Phase Space

Selection

e+ T2

PT

Calorimeter

Compton Transmission Polarimeter

Ee = 6.3 MeV Ie = 1 µA T1 = 1 mm W

Geant4

PEPPo

J. Dumas, PhD Thesis (2011)

PEPPo measured the longitudinal polarization transfer from 8.25 MeV/c e- to e+ in the 3.07-6.25 MeV/c momentum range.

Principle of Operation

Proof-of-principle experiment Eric Voutier

Compton Transmission Polarimeter

FADC 250

Hamamatsu R6236-100

Ø CsI crystals a (6×6×28 cm3) are coupled to PMTs equiped with custom amplified bases 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 FADC250 that sampled the signal at 250 MHz.

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).

Electron and positron polarimetry 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 (Hampton University)

Eric Voutier

10/17

Electron and positron polarimetry

G. Alexander et al., NIMA 610 (2009) 451

Paphos, November 1st-7th, 2015 PT = 7.06% ± 0.05%Stat. ± 0.07%Syst.

PEPPo Measurements

• PEPPo operation

• Polarized positron characterization


PEPPo operation Eric Voutier


Ø The location of the 511 keV peak is used for in-situ monitoring of the effective gain of the read-out chain, and provides a link to radioactive source calibration data.

Ø Compton physics asymmetries are obtained from the polarization sensitive energy

deposit spectra in the central crystal.

Ø The coincidence time spectra allow for accidental subtraction.

Eric Voutier

511 keV from e+ annihilation at rest

Bremsstrahlung end-point

Energy (FADC units)

Energy Deposit Spectra


PEPPo operation

Positron Analyzing Power

Ø GEANT4 simulations allow to link the measured electron analyzing power to the expected positron analyzing power of the PEPPo Compton transmission polarimeter.

Eric Voutier Polarized positron characterization


A. Adeyemi (Hampton University)

Ø Positron polarization is determined using measured electron beam and target polarizations, the polarimeter’s measured electron analyzing power, the measured experimental asymmetry for e+, and the GEANT4 deduced e+ analyzing power.

Positron Polarization

Eric Voutier Polarized positron characterization


Ø Significant non-zero experimental asymmetries increasing with positron momentum indicate efficient polarization transfer from electrons to positrons.

D. Abbott1, P. Adderley1, A. Adeyemi3, P. Aguilera1, M. Ali1, H. Areti1, M. Baylac2, J. Benesch1, G. Bosson2, B. Cade1, A. Camsonne1, L. Cardman1, J. Clark1, P. Cole4, S. Covert1, C. Cuevas1, O. Dadoun5, D. Dale4, H. Dong1, J. Dumas1,2, E. Fanchini2, T. Forest4, E. Forman1, A. Freyberger1, E. Froidefond2, S. Golge6, J. Grames1,

P. Guèye3, J. Hansknecht1, P. Harrell1, J. Hoskins14, C. Hyde7, B. Josey13, R. Kazimi1, Y. Kim1,4, D. Machie1, K. Mahoney1, R. Mammei1, M. Marton2, J. McCarter11,

M. McCaughan1, M. McHugh10, D. McNulty4, T. Michaelides1, R. Michaels1, B. Moffit1, C. Muñoz Camacho8, J.-F. Muraz2, K. Myers9, A. Opper14, M. Poelker1,

J.-S. Réal2, L. Richardson1, S. Setiniyazi5, M. Stutzman1, R. Suleiman1, C. Tennant1, C.-Y. Tsai12, D. Turner1, A. Variola5, E. Voutier2,8, Y. Wang1, Y. Zhang9

1 Jefferson Lab, Newport News, VA, US 2 LPSC, Grenoble, France 4 Hampton University, Hampton, VA, USA 5 Idaho State University & IAC, Pocatello, ID, USA 3 LAL, Orsay, France

6 North Carolina University, Durham, NC, USA 7 Old Dominion University, Norfolk, VA, US 11 IPN, Orsay, France 12 Rutgers University, Piscataway, NJ, USA

8 The College of William & Mary, Williamsburg, VA, USA 9 University of Virginia, Charlottesville, VA, USA 13 Virginia Tech, Blacksburg, VA, USA 14University of New Mexico

10 George Washington University, Washington, DC, USA

PEPPo Collaboration

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 Paphos, November 1st-7th, 2015

Outlook

Summary

Polarized and unpolarized positron beam provide important complementary capabilities for the achievement of the hadronic physics

program at JLab.

2g physics, GPDs…

Eric Voutier


The PEPPo experiment @ the CEBAF injector has been a first step

in an R&D effort for a polarized positron beam at JLab.

17/17

PEPPo II is building-up with the aim of developing a polarized e+ beam for CLAS12 Ee+ > 4 GeV Ie+ > 10 nA Pe+ > 50%

Please join !!

Ultra-relativistic approximation

H. Olsen, L. Maximon, PR114 (1959) 887

Ø The most currently used framework to evaluate polarization transfer for polarized bremsstrahlung and pair creation processes is the O&M work developped in the Born

approximation for relativistic particles and small scattering angles.

Bremsstrahlung and Pair Creation

BREMSSTRAHLUNG PAIR CREATION

Eric Voutier

E.A. Kuraev, Y.M. Bystritskiy, M. Shatnev, E. Tomasi-Gustafsson, PRC 81 (2010) 055208

Bremsstrahlung and Pair Creation

Polarization transfer physics

BREMSSTRAHLUNG PAIR CREATION

Ø These reference processes have been revisited considering the finite mass of the leptons, generating additional terms to the leptonic tensor.

Eric Voutier

Magnetic Flux Measurement

Eric Voutier

PT = 7.06% ± 0.05%Stat. ± 0.07%Syst.

Ø The iron core target is equipped with 3 pick-up coils measuring the magnetic flux generated by the magnet current variation (ramping-up, polarity reversal).

Ø Specific cycling procedures are used during the experiment to monitor the target polarization.

E. Froidefond, E. Voutier, PEPPo TN-14-02 (2014)

22/36

Electron and positron polarimetry

peppo · 2016. 12. 28. · j. grames, e. voutier et al., jlab experiment e12-11-105, 2011 polarized...

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