Transcript Slide 1

Polarized Antiprotons –
the Quest for a Missing Tool
Erhard Steffens
Physikalisches Institut, University of Erlangen-Nürnberg
[email protected]
•Motivation
•History
•FAIR and PAX
•Recent Workshops
- Workshop at Cockcroft Institute (August 2007)
- Heraeus Seminar at Physik Haus (June 2008)
•New results on depolarization study at COSY
•Conclusions
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Motivation
Our Knowledge about pp interaction is limited: lack of
polarization data! Restricted to single-spin (A0n00, A000n) data.
Attempts at LEAR (1983-1996) to produce polarized stored p ' s
were unsuccessful!
FAIR project: Facility for Antiproton and Ion Research. New
chance after the LEAR program to study antiproton physics in
a broad energy range from traps to Super-LEAR (= HESR).
Revival of ideas about stored polarized antiprotons: PAX
experiment at FAIR.
Outstanding physics case – see PAX proposal, and talks at this
meeting (e.g. Anselmino on Tue.).
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History of Polarized Anti-Protons*
Early 1980‘s: CERN S pp S collider and its powerful p -source.
Enabled a low-energy program at LEAR (stretcher and storage
ring). First ideas by Kilian and Möhl on polarizing p ' s by Spin
Filtering.
Spin filtering was proposed by Shapiro in 1966 to polarize
thermal neutrons by spin-dependent attenuation in a
polarized hydrogen target.
now standard method in neutron physics using polarized 3He gas cells
First successful test reported at the Madison conference
(1970): intense neutron beam from a nuclear underground
explosion polarized by means of a DNP proton target.
*) see Proc. of the Workshop on Polarized Antiprotons Beams –How? – AIP Conf. Proc. 1008 (2008) p.1
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Spin Filtering
B.C. Diven: Nuclear Explosions as
a Nuclear Physics Tool. Ann. Rev.
Nucl. Sci. 20 (1970) 79.
Tower above the line of sight to a nuclear explosion,
housing the different experiments
Five neutron beams were extracted from the nuclear explosion and utilized. The tower on rails could be
withdrawn within a few minutes after the explosion from the expected region of ground collapse. In such
a tower, the first Spin Filtering experiment has been performed at the end of the 1960‘s.
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Workshop at Bodega Bay*
List of topics discussed at the workshop:
1. Polarized antiprotons from the decay in flight of antihyperons
2. Spin filtering of antiprotons by a polarized hydrogen target in a storage ring
3. Stochastic techniques à la ‘Stochastic Cooling’
4. DNP in flight using polarized electrons and microwave radiation
5. Spontaneous Spin-Flip synchrotron radiation
6. Spin-Flip synchrotron radiation induced by X-ray laser
7. Polarization by scattering
8. Repeated Stern-Gerlach deflection
9. Polarized antiprotons via the formation of antihydrogen and application of the ABS
method
10. Polarizing during storage in a Penning trap
11. Polarizing by Channeling
12. Polarizing through interaction with polarized X-rays from a diamond crystal
*) Proc. Workshop on Polarized Antiprotons, Bodega Bay, CA, 1985. A.D. Krisch, A.M.T. Lin, O. Chamberlain (Edts.),
AIP Conf. Proc. 145 (1986) 207
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FILTEX
CERN proposal CERN/PSCC/85-80 (Nov. 5, 1985)
E. St. et al, Proc. 3rd LEAR workshop Tignes 1985, p. 245:
„Proposal for measurement of spin dependence of the pp
interaction at low momenta“
•Spin Filtering test experiment prepared for the Heidelberg TSR
by the FILTEX collaboration (Heidelberg-Karlsruhe-MadisonMainz-Rutgers-München).
•Polarized hydrogen Filter target of unprecedented density
(1014 atoms/cm3) to be developed.
•1992 proof-of-principle: build-up of polarization of stored
23MeV protons observed!
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FILTEX test experiment at TSR (Heidelberg)
• Principle of SpinFiltering
• Polarized hydrogen
target and detectors
at the TSR
• Target chamber and
cooled storage cell
• Result on
polarization build-up
(the only experimental
result so far)
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FILTEX test experiment at TSR (Heidelberg)
• Result on polarization build-up (the only
experimental result so far)
• Build-up rate was ≈ 1/2 of the naive expectation
(nuclear interaction only)
• Quantitative explanation by H.O. Meyer and C.J.
Horowitz [e.g. PRL 72 (1994) 3981]. Two more
contributions introduced: from polarized electrons,
and by scattering into acceptance of the storage ring
• New Proposal by PAX collaboration [F. Rathmann et al, PRL 94 (2005) 014801],
solely based on spin-transfer from polarized (bound) electrons: calculable
interaction! more efficient!
• New Proposal by Mainz group (Th. Walcher, H. Arenhövel, K. Aulenbacher et al) to
utilize Spin-transfer from free positrons to co-moving antiprotons at low relative
velocity [e.g. Eur. Phys. J. A34 (2007) 447] – no losses!
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FAIR and PAX
• FAIR: Facility for Antiproton and Ion Research
– first beams in 2013(?)
• Antiproton source:
SIS100, production target,
collector (CR) and
accumulator (RESR) rings
• HESR: 15GeV/c
antiproton storage ring
(PANDA and possibly PAX)
APR
• APR: Antiproton
Polarizer Ring for spin
filtering of antiprotons
• PAX: Direct
measurement of
transversity in double
polarized Drell-Yan (see
talk Anselmino)
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FILTEX test experiment at TSR (Heidelberg)
•Result on polarization build-up (the only
experimental result so far)
• Build-up rate was ≈ 1/2 of the naive expectation
(nuclear interaction only)
• Quantitative explanation by H.O. Meyer and C.J.
Horowitz [e.g. PRL 72 (1994) 3981]. Two more
contributions introduced: from polarized electrons,
and by scattering into acceptance of the storage ring
•New Proposal by PAX collaboration [F. Rathmann et al, PRL 94 (2005) 014801],
solely based on spin-transfer from polarized (bound) electrons: calculable
interaction! more efficient!
• New Proposal by Mainz group (Th. Walcher, H. Arenhövel, K. Aulenbacher et al) to
utilize Spin-transfer from free positrons to co-moving antiprotons at low relative
velocity [e.g. Eur. Phys. J. A34 (2007) 447] – no losses!
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Polarizing Mechanisms
• Trivial non-selective losses occur at gas target: single-scattering Coulomb losses. to be minimized!
• Protons scattered off free electrons stay within acceptance!
I/I0
a lot of open
questions!
0.8
P
0.6
spin-transfer by free
electrons: no losses!
0.4
0.2
0
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Recent Workshops
August 29-31, 2007 – Cockcoft Institute, Daresbury (UK)
Polarized Antiproton Beams – How?
S. Chattopadhyay, D.P. Barber, N. Buttimore, G. Court, E. St. (Organizers)
AIP Conf. Proc. 1008 (2008)
June 23-25, 2008 – Physik Haus, Bad Honnef (GER)
409. WE-Heraeus-Seminar: Polarized Antiprotons
P. Lenisa & F. Rathmann; talks online at
http://www.fe.infn.it/heraeus/program.html
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Polarized Antiproton Beams – How?
Key issues
• How to understand the FILTEX result?
• Discussion of alternative methods.
- Hosted by the Cockcroft Insitute
(Daresbury Campus, Warrington, UK)
- S. Chattopadhyay (Liverpool and CI)
- About 30 participants and speakers
S. Chattopadhyay, D.P. Barber, N. Buttimore, G. Court, E. St.
(Edts.) AIP Conf. Proc. 1008 (2008)
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How to explain the FILTEX results?
• Clarification of possible mechanisms
N. Buttimore (Dublin): Analysis of Channelling, and of
polarization transfer by polarized leptons
D. O‘Brien (Dublin): Analysis of spin filtering, evolution
equation
• Analytical calculations based on NN and el.-magn. interaction
V. Strakhovenko (Novosibirsk)
• Analysis of el.-magn. spin-flip amplitude
K. Nikolenko (FZ Jülich - talk presented by F. Rathmann)
→ exact cancellation of spin-flip and ‚scattering into acceptance‘
which would eleminate Meyer‘s 1994 re-analysis of the FILEX result
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Spin transfer by free polarized electron
• New method proposed by T. Walcher, H. Arenhoevel et al
(Mainz): Eur. Phys. J. A34 (2007) 447.
• Huge spin transfer cross section (H. Arenhoevel 2007) in
attractive systems like e  p or e  p predicted: 1013 barn at
low relative velocities!
• Does not contradict slow polarization
build-up with

polarized electrons of the H target at rest and 23MeV
protons.
• Would enable fast loss-free build-up of polarization!
→ found during the workshop: different 3-spin quantity to be calculated
instead of the 2-spin quantity considered
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Alternative methods
Spin Splitter: separation of stored particles in opposite spin states
by the repeated Stern-Gerlach effect (discussed already at Bodega Bay)
D. Barber (DESY and CI): no experimental evidence yet. ‚Proofs‘ by
means of simulations should be taken with great care due to the
smallness of the underlying SG effect.
DNP in Flight: Spin transfer between co-moving antiprotons and
electrons induced by rf, analoguous to DNP.
A. Krisch (Michigan): sketched a possible test set-up based on the
ideas discussed at Bodega Bay (C. Jeffries). Not clear whether the
conditions could be met.
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Alternative methods
Polarizing by Channelling through bent crystals: Idea is that due
to continuous scattering
to one
side, a polarization
of the projecnothing
in common
with
tile is accumulated . old channelling results
discussed
in the
past examples which
M. Ukhanov (Protvino):
presented
numerical
(M. Kaminsky 1969)
would lead to high polarization – based on completely modeldependent assumptions. Experiments required!
M. Fiorini (Ferrara): Experimental studies of channelling, in
particular by bent crystals used for the deflection of multi-TeV
ion beams (halo clearing at the LHC?).
→ Channelling through bent crystals works (polarization to be
measured)
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Cockcroft workshop: Conclusions
H.-O. Meyer (Indiana) in his summary talk:
Scientists have produced a large variety of polarized beams
(p, n, d, 3He, 6Li, 7Li, 23Na and targets incl. 3He and Holmium!
Even if polarized antiprotons offer so much resistance, we
should not give up!
Without empirical back-up it is equally difficult to dismiss a
subject or to accept it!
The only option is to improve the theoretical basis, until a
supporting or refuting measurement can be identified.
At present, the best bet seem to be methods involving a
storage ring and an internal target.
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409. WE-Heraeus-Seminar
Polarized Antiprotons
June 23-25, 2008
Conveners: P. Lenisa (Ferrara) and F. Rathmann (FZ Jülich)
• Present understanding of Spin Filtering
- Rith, Strakovenko, Walcher, Haidenbauer
• Spin filtering experiments
- Nekipelov, Oellers, Nass, Prasuhn, Aulenbacher, Schleichert, Belochitsky
• Physics with polarized antiprotons
- Koop, Ratcliffe, Melis, Tomasi-Gustafson, Kroll
• Spin physics experiments
- Meyer, Contalbrigo, Bradamante, Schäfer, Metz, Cisbani, Maas
• Other antiproton physics topics
- Knie, Shevchenko, Oelert, Lehrach, St. & Stroeher (Summary)
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Heraeus Seminar: News
New calculation of the relevant spin transfer cross section by
Arenhoevel. Same order of magnitude found: 1013 barn = 10-11 cm2 !
• Is the numerics stable at these low relative velocities? Note that
experience with electron cooling tells us that at vrel = 0
depolarization is very low!
• How can a process based on
dipole-dipole interaction reach
out as far as rint ≈ 18nm?
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Heraeus Seminar: News
D. Oellers (Jülich): Measurement of the depolarizing p-e cross
section using co-moving electrons (see talk F. Rathmann Tue.)
• Idea: Electrons at the appropriate vrel should depolarize
circulating protons at a comparable rate!
• Use Cooler electrons detuned to the right vrel to check the
Arenhoevel prediction.
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taken from talk F. Rathmann
Depolarization Studies at COSY: Idea
• Use proton beam and co-moving electrons
• Turn experiment around: p e  p into p e  p
i.e. observe depolarization of a polarized proton beam
COSY
electron
Velocity
cooler
(detuned)
mismatch
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taken from talk F. Rathmann
Depolarization Studies at COSY: Results
Nominal proton energy in electron rest frame (keV)
0
1
2
3
depol (barn)
4107
2107
0
-2107
-4107
0
110-3
210-3
310-3
|Relative velocity of electrons in proton rest frame| (c)
No effect observed
measured cross section at least 6 orders-of-magnitude smaller than predicted 1013 b
Heraeus Seminar: News
D. Oellers (Jülich): Measurement of the depolarizing p-e cross
section using co-moving electrons (see talk F. Rathmann Tue.)
•Electrons at the appropriate vrel should depolarize circulating
protons at a comparable rate!
• Use Cooler electrons detuned to the right vrel to check the
Arenhoevel prediction.
• Present results indicate that Spin Transfer from polarized
free electrons to co-moving protons has a cross section of at
most 107 barn.
• Note that analytical calculations by the Novosibirsk group
exist: effect should be negligible (see Proc. Cockcroft workshop)
→ Loss-free polarization build-up of protons (antiprotons) by
free polarized electrons (positrons) is not an option! 
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Present picture
• Spin Filtering of protons is solely based on NN interaction!
• The build-up of ‚high‘ polarization in the order of ≥ 0.2
requires a low-beta section (b ≤ 0.3m) in order to minimize
the Coulomb losses → Experimental demonstration with
protons at COSY.
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taken from talk F. Rathmann
Spin-filtering at COSY: Optimize, understand FILTEX
p
pp = 0.3… GeV/c
Superconducting
quadrupole
(new)
Need a
„low-ß section“
in COSY
ABS + storage cell,
Si-tracking det´s
(HERMES)
Present picture
•Spin Filtering of protons is solely based on NN interaction!
• The build-up of ‚high‘ polarization in the order of ≥ 0.2
requires a low-beta section (b ≤ 0.3m) in order to minimize
the Coulomb losses → Experimental demonstration with
protons at COSY.
• The layout of an antiproton polarizer ring (APR) requires to study
spin filtering of antiprotons.
• The Antiproton Deccelerator ring at CERN is the only option for
the near future – ongoing collaboration of PAX with AD machine
physicists to work out a realistic plan.
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Outlook
Spin filtering studies at COSY (FZ Jülich) with protons:
• determine & optimize beam lifetime: required for long filtering times
(next beam time in Nov. 2008);
• set up HERMES-ABS and recoil detectors (ready in 2009);
• implement set-up in ring (2010-11), perform measurements.
Spin filtering studies at AD (CERN) with antiprotons:
• full proposal worked out and submitted to CERN,
• move equipment, repeat experiments with antiprotons (≈ 2011-12):
 By 2012/13 we know how best to do spin-filtering with p !
• Design the APR: ready for PAX at FAIR!
Let us work together in order to add a missing,
very powerful instrument to our tool box!
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