Do unpolarized electrons affect the polarization of a stored proton beam?

1. Do unpolarized electrons affect the polarization of a stored proton beam? How to produce polarized antiprotons - and what to use them for? October 7, 2008 | Frank Rathmann (for the ANKE and PAX collaborations) SPIN 2008 (Charlottesville, Virginia, USA)

2. Introduction ~ 3 years ago, we proposed a method to polarize antiprotons by „spin-filtering“

3. Introduction New initiative, driven by the FAIR-project at GSI

4. Introduction (How) is it possible to provide polarized antiproton beams in HESR ? High Energy Storage Ring (HESR) for a beam of antiprotons

5. Plan of talk • The (long) road to polarized antiprotons: • Proposals, ideas, calculations, … • Experiments • Depolarization studies at COSY • FILTEX (TSR) • Spin-filtering at COSY (see talk by A. Nass) • Spin-filtering at AD/CERN • Summary, Conclusion … taken on by the PAX-collaboration Spokespersons: F. Rathmann (Jülich), P. Lenisa (Ferrara)

6. Two Methods: Loss versus spin flip For an ensemble of spin ½ particles with projections +() and - ()

7. Proposed methods (1): Some history … EPAC 1988 • Stern-Gerlach splitting never tried (huge effort)

8. Proposed methods (2): Recent paper • Need for an experimental test of this idea !

9. 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 Velocity mismatch COSYelectron cooler(detuned)

10. Depolarization Studies at COSY: Principle (1) • Use (transversely)polarized proton beam circulating in COSY • Switch on (detuned)electron cooler to depolarize proton beam • Analyze proton polarization with internal D2-cluster target of ANKE ANKE cluster target & STT e-cooler p Tp = 49.3 MeV

11. Depolarization Studies at COSY: Principle (2) After detuning, proton energy slowly follows electron energy: U = 245 V  ve = 1.5·10-3 c fR = 40 Hz in 5 s: vp/ ve~0.03 Detuning e-cooler for 5 s only ensures that proton momentum stays fixed.

12. tuned cycle detuned cycle Target off Target on 27095 4  108 Ecooler Voltage (V) Number of Beam Particles Telectron-off 50·5 s Tdetuned 50·5 s +245 2  108 26850 Tnominal 50·5 s Tnominal 50·5 s 1000 0 200 400 600 800 1000 0 200 400 600 800 time (s) Compare cycle-by-cycle: No electrons to detuned electrons Depolarization Studies at COSY: Cycle setup

13. 0 Ptuned Pdetuned Beam current Depolarization Studies at COSY: Super Cycle DeterminePtunedandPdetunedfrom identical cycles, except for detuned cooler

14. p D2 Depolarization Studies at COSY: Polarimetry (Experiment carried out in March 2008) pd elastic scattering:detection in two (L-R) symmetric Silicon Tracking Telescopes Deuteron identification d p

15. Tuned and detuned beam polarizations 0.6 Beam Polarization 0.4 tuned cooler 0.2 detuned cooler 0 -4 -3 -2 -1 0 1 2 3 4 Proton kinetic energy in electron rest frame (keV) p D2 Depolarization Studies at COSY: Results (1) pd elastic scattering:detection in two (L-R) symmetric silicon tracking telescopes

16. Measured ratio of polarizations vs Proton Kinetic energy in electron rest frame 1.2 Pdetuned/Ptuned 1 0.8 -4 -3 -2 -1 0 1 2 3 4 Nominal proton kinetic energy in electron rest frame (keV) p D2 Depolarization Studies at COSY: Results (2) pd elastic scattering:detection in two (L-R) symmetric silicon tracking telescopes

17. Thermal transverse motion of electrons in the ecooler: experiment measuresmixture Depolarization Studies at COSY: Results (3) measured Weight functions  and (1- ) from 3D Maxwellian electron velocity distributions

18. Depolarization Studies at COSY: Results (4) Nominal proton energy in electron rest frame (keV) 0 1 2 3 4107 Preliminary 2107 depol (barn) 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

19. Depolarization Studies at COSY: Results (5)Systematic errors • Total measurement error dominated by statistics. Preliminary • Systematic errors of polarization determination in progress.

20. Depolarization Studies at COSY: New calc´s (NIM B) 10.1016/JNIMB.2008.04.010 ~ 1 mb  No effect expected !

21. Spin-filtering: Polarization build-up of an originally unpolarized particle beam by repeated interaction with polarized hydrogen target, e.g. in a storage ring: Spin-filtering is known to work („FILTEX“)

22. Spin-filtering at TSR: „FILTEX“ – proof-of-principle F. Rathmann. et al., PRL 71, 1379 (1993) Spin filtering works for protons

23. Spin-filtering at COSY: Optimize, understand FILTEX p Need a „low-ß section“ in COSY pp = 0.3… GeV/c ABS + storage cell, Si-tracking det´s (HERMES) Superconducting quadrupole (new)

24. 4 3 2 1 Spin-filtering at COSY: Low-ß Section Target: Storage cell Polarimeter  Need superconducting quadrupoles

25. Spin-filtering at CERN/AD: pp and pd scattering • Target (equipment used, tested at COSY) • Electron cooler (upgrade of existing AD-cooler) • Snake (also longitudinal; new) • Measurement of effective p polarization build-up cross section • First measurement of spin-correlations in above reactions

26. Expectations for AD • AD machine acceptance: Ax = 180 m, Ay = 200 m • Cooled 2 beam emittance = 1 m • Realistic calculation of acc(mrad) using AD lattice functions from Pavel Belochitsky and triangular density distribution in storage cell • Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991) • Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995)

27. Expectations for AD (Filtering for two beam lifetimes) transverse longitudinal 0.1 0.08 0.15 0.06 A 0.1 0.04 10 mm, 7.4 mrad 12 mm, 8.9 mrad 0.05 14 mm, 10.5 mrad 0.02 16 mm, 12.0 mrad 10 mm, 25 mrad 10 mm, 50 mrad 0 Polarization (2·b) 0 100 200 300 100 200 300 0.15 0.02 D 0.1 0.01 0.05 0 0 100 200 300 100 200 300 Beam kinetic energy (MeV)

28. Spin-filtering at COSY: Milestones, timeline • COSY: determine / optimize beam lifetime: • needed for large filtering time (beamtime in II/2008) • SC quadrupoles – design almost ready; companies have been contacted (order in 2008) • COSY: set up HERMES-ABS and recoil detectors (2009) • COSY: implement set-up in ring (2010-11), perform sf-measurements • CERN/AD: LoI  full proposal; move equipment and repeat with anti-protons (~ 2011-12)  By 2012/13 know how best to do spin-filtering with p!! • Design the APR (antiproton polarizer ring)

29. Summary: p e- p e+ p p p p long. trans. WAKBJ: gigantic ??? MSS: small small 1016

30. Summary: p e- p e+ p p p p long. trans. WAKBJ: gigantic ??? MSS: small small No depolarization of polarized protons

31. Summary: Spin-filtering works: p (FILTEX)  COSY p  CERN/AD p e- p e+ p p p p long. trans. WAKBJ: gigantic ??? MSS: small small No depolarization of polarized protons

32. Conclusion: • The road towards polarized antiprotons is long … • But: - clear roadmap - commitment by PAX-collaboration - first measurements/achievements • We appreciate any help! • Note: Now and here (expertise) or „never“ (not in a very long time)!

33. Spares

34. Hadron Physics „Dream Machine“ for FAIR: … an asymmetric (double-polarized) proton (15 GeV/c) – antiproton (3.5 GeV/c) collider using HESR, CSR and APR

35. Quark Transversity Distribution in Drell-Yan: Double transverse spin asymmetry: First direct measurement: No competitive processes

36. Cooler on and off

37. Spin-filtering at TSR: „FILTEX“ TSR … Test Storage Ring at MPI Heidelberg FILTEX … Filter Experiment (1992)