peppo · 2016. 12. 28. · j. grames, e. voutier et al., jlab experiment e12-11-105, 2011 polarized...
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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
Paphos, November 1st-7th, 2015
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 ±±+=
( ) [ ] ( )[ ]( )31~,~~12 FGfGGGGGP EMMEMEtR ddd
tees ±±
--=
( )[ ]( )3222 ~,~21 FGfGGP MMMlR ddes ±-=
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
Paphos, November 1st-7th, 2015
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
Paphos, November 1st-7th, 2015
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.
7/17 Paphos, November 1st-7th, 2015
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
8/17 Paphos, November 1st-7th, 2015
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
9/17 Paphos, November 1st-7th, 2015
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
Paphos, November 1st-7th, 2015
PEPPo operation Eric Voutier
12/17 Paphos, November 1st-7th, 2015
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
13/17 Paphos, November 1st-7th, 2015
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
14/17 Paphos, November 1st-7th, 2015
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
15/17 Paphos, November 1st-7th, 2015
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
Paphos, November 1st-7th, 2015
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