Note on the History of Polarized Antiprotons

Erhard Steffens, University of Erlangen-Nürnberg, Germany.

A number of ideas have been put forward for producing polarized nucleons via interaction with a polarized target. In 1966 Shapiro (see ref.1) pointed out that owing to the strong spin dependence in the (n,p) interaction, polarized neutrons could be produced in a way which today is called ‘Spin Filtering’. In 1970, a first test, utilizing an underground nuclear explosion as a polarized neutron source, was reported [1]. Of course, the equipment including the solid polarized target was destroyed during the experiment, making it a rather expensive method. It is worth noting that the most effective method, to date, for polarizing beams of thermal neutrons is Spin Filtering on a high-pressure polarized 3He gas target [2]. This results in high transmission and polarization.   Spin filtering of protons stored in the ISR (CERN) was proposed by Csonka in 1968 [3].  After the discovery of the antiproton in 1955 by Chamberlain, Segre and others, the interaction of antiprotons with nuclei was studied using secondary beams at various laboratories (BNL, CERN, FNAL, Serpukhov, KEK). In the early 1980's the CERN antiproton source project enabled the first storage of antiprotons in collector and experimental storage rings like the SpS collider. Then, in 1982 Kilian and Möhl proposed spin filtering of antiprotons in the low-energy antiproton cooler ring LEAR [4] and in 1984 Povh, Steffens and Walcher developed the correct theory and a realistic proposal for LEAR and suggested a test with protons at the Heidelberg test storage ring TSR . This was presented at the 3rd Lear workshop in January 1985 [5]. In 1985 the famous workshop at Bodega Bay (CA, USA) took place [6], organized by O. Chamberlain and A. Krisch and attended by 21 scientists, the number of which was limited by the capacity of the hotel. The four-day meeting was organized in plenary and group sessions and aimed at a thorough discussion of all ideas currently on the market or in the air. In his summary, A. Krisch presented twelve ideas:

  1. Polarized ’s from the decay in flight of antihyperons
  2. Spin filtering of  ’s on a polarized hydrogen target in a cooler 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 an X-ray laser
  7. Polarization by scattering
  8. Repeated Stern-Gerlach deflection
  9. Polarized ’s 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

Several of these ideas survived the workshop for a significant period of time. In particular, idea (1) has been successfully applied at FNAL by the E-704 Collaboration [7], leading to secondary high-energy beams of polarized protons and antiprotons up to 500 GeV/c in momentum. No accumulation and storage has been attempted. Idea (2) was rated as practical and promising. Spin filtering on a polarized hydrogen gas target has been the basis of an experimental program conducted by the FILTEX Collaboration. In 1992, the proton test experiment took place with 23 MeV stored protons at the TSR (Heidelberg) demonstrating for the first time that this method works in principle [8] (see note by F. Rathmann). This idea was taken up in 2004 by the PAX Collaboration for application at the future antiproton facility at FAIR (Darmstadt). Because of lack of experimental work in the last 15 years, there is still a considerable uncertainty about the filtering mechanism and whether additional processes contribute. Such a contribution, spin-transfer from polarized electrons to the stored proton beam, was proposed by Meyer in 1994 [9]. Methods for utilizing this electromagnetic, and thus calculable, process for polarizing stored beams are currently under discussion.  Proton scattering off carbon is a well-known polarizer. The straight-forward idea (7) for polarizing antiprotons in the same way was tested at LEAR [10] but the measured polarization was too low for its application as an antiproton polarizer.   The theory of the ‘Spin Splitter’ (8) has been discussed in a number of papers, e.g. [11], and workshop contributions. No experimental demonstration has been provided yet. There is a revival of interest in idea (11) due to progress in channeling of high-energy particles.   It remains to be seen if and how these past efforts will result in a powerful tool for the study of the spin-dependence of antiproton interactions. References
  1. G.A. Keyworth and J.R. Lemley, in: Proc. 3rd Int. Symp. on Polarization Phenomena in Nuclear Reactions, Madison, 1970, p. 873
  2. K.P. Coulter et al., NIM A 288 (1990) 463
  3. P.L. Csonka, NIM 63 (1968) 247
  4. K. Kilian and D. Möhl, in: Proc. 2nd LEAR Workshop, Erice, 1982, p.701
  5. E. Steffens et al., in: Proc. 3rd LEAR Workshop, Tignes, 1985, p.245; and CERN Proposal CERN/PSCC/85-80 (Nov. 5, 1985)
  6. Proc. of the Workshop on Polarized Antiprotons, Bodega Bay, CA, 1985. A.D. Krisch, A.M.T. Lin, O. Chamberlain (Edts.), AIP Conf. Proc. No. 145 (1986) p. 207
  7. A. Yokosawa, in: Proc. 8th Int. Symp. on High-Energy Spin Physics, Minneapolis, 1988. K.J. Heller (Edt.), AIP Conf. Proc. No. 187 (1989) p. 210
  8. F. Rathmann et al., PRL 71 (1993) 1379
  9. C.J. Horowitz and H.O. Meyer, PRL 72 (1994) 3981
  10. A. Martin et al., Nucl. Phys. A 487 (1988) 563
  11. T.O. Niinikoski and R. Rossmanith, NIM A 255 (1987) 460
If there are any queries or comments on this note please contact me via  polanti-p@dl.ac.uk

 

  
     
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