Polarization transfer mechanism as a possible source of the polarized antiprotons

M.A. Chetvertkov1, V.A. Chetvertkova2, S.B. Nurushev3

1. Moscow State University, Moscow ,Russia2. Skobelitsyn Institute of nuclear physics, Moscow State

University, Moscow, Russia3. Institute of high energy physics, Protvino, Russia

AbstractWe suggest to study the polarization transfer mechanism in the inclusive

reaction of the antiproton production by the polarized proton beam. As a basis of the

experimental set-up we foresee the standard source of the unpolarized antiprotons

as it was realized at PS CERN. This scheme should be transformed by three major

modifications: 1) instead of the initial unpolarized proton beam we shall use the

longitudinally ( transversally) polarized proton beam, 2) transform the longitudinal

polarization of the produced antiprotons to the transverse polarization, and 3) build

the polarimeter for the polarized antiprotons of the proper emerges. We assume that

the best place for such research will be AGS at the Brookhaven National Laboratory

having almost all the needed infrastructures. In the case of revealing the large

polarization transfer tensor we may get the new source of the polarized antiprotons. If

this tensor appears to be small but non zero the production of the antiprotons by the

polarized (longitudinally or transversally) proton beam might become beneficial for

the filtering technique.

Contents

1. Introduction 2. Experimental evidences for the

polarization transfer mechanism 3. Scheme of producing the unpolarized

antiprotons 4. Proposal of the experiments for measuring

the polarization transfer from protons to antiprotons

5. Conclusions

1. IntroductionThe problem of producing the intense polarized antiproton source with the appropriate

polarization becomes very acute at present. Such interest is instigated by the great potential of

the physics with the polarized antiprotons [PAX(2005)]. Approximately a dozen suggestions

were made about how to get the polarized antiprotons [Krisch (1985)], [Steffens(2008)] but

none of them (exclusion is the filtering technique [Rathmann(2005)]) was experimentally

demonstrated as really working tool.

The following is the list of these suggestions:

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 (Dynamic Nuclear Polarization) in flight using polarized electrons and microwave

radiation

5.Spontaneous Spin-Flip synchrotron radiation

6.Spin-Flip synchrotron radiation induced by X-ray laser2005

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.

In this presentation we propose the very well known (at low energy) method of producing the

polarized beam - the mechanism of the spin transfer to the secondary particles from the

primary polarized beam. In section 2 we remind the several experiments providing the

evidences for the spin transfer mechanism at low and high energy ranges. In the same

section we make the statement that there is no any theoretical estimate of the spin transfer

tensor from polarized protons to the antiprotons and no any experimental evidence for

measuring such tensors.

Therefore we suggest the experiment at AGS for measuring the spin transfer tensor from

the polarized protons to the secondary antiprotons produced at zero degree. In Section 3

we recall the standard technique of obtaining the unpolarized antiprotons by the

unpolarized primary proton beam according to PS CERN scheme [The Antiproton Source

Rookie Book, 1999, Version 1.1]. Then in Section 4 we modify this scheme to produce the

polarized antiprotons by the polarized proton beam. We also propose the schemes of

measuring the spin transfer tensor at pbar production at zero angle as a function of the

antiproton momentum.

In Conclusions we summarize the results of our study of the possible new source of the

polarized antiprotons.

2. Experimental evidences for the polarization transfer mechanism

There is no any theoretical or experimental paper devoted to the direct prediction or proof of the existence of the polarization transfer mechanism in the inclusive reaction

,XpNp

where the arrows indicate the polarization of the corresponding particle.

2a. Spin Transfer tensor in Inclusive 0 Production by Transversely Polarized

Protons at 200 GeV/c[A. Bravar et al., Spin Transfer in Inclusive 0 Production by Transversely

Polarized Protons at 200 GeV/c, Phys. Rev. Lett., vol. 78, number 21, 4003-4006]

This is the first and only example of non-zero Spin Transfer Mechanism, experimentally established at 200 GeV/c (which is equivalent to the √S≈20 Gev). The depolarization tensor DNN (Wolfenstein’s parameter)=KN0;N0 (according to the Ann Arbor convention) in the reaction

Xpp 0

has been measured with the transversely polarized protons at 200 GeV/c over a wide xF range and a moderate pT (E704 experiment at FNAL). DNN reaches positive values of about 30% at high xF and pT ~ 1.0 GeV/c. This result proves the existence of the essential spin transfer mechanism at sufficiently high energy..

Figure 3. Depolarization DNN data as a function of pT in Xpp 0

at 200 GeV/c. The errors shown are statistical only.

Longitudinal spin transfer of Lambda and antiLambda in pp collisions at STAR

[Qinghua Xu (Shandong Uni.) for the STAR collaboration

Dubna Spin workshop, September 4, 2009]

3. Scheme of producing the unpolarized antiprotons

[ H. Koziol, S. Maury, Parameter List for the Antiproton Accumulator Complex (AAC), Edition 1994, CERN, Geneva, Switzerland]

Scheme of Antiproton Accumulator Complex (AAC), CERN.

Parameters of the AAC.

Proton and antiproton beam transport lines at AGS

The best way of doing the measurement of the spin transfer tensor from the polarized protons to the antiprotons would be this PS CERN scheme. But PS has no polarized proton beam. Therefore we think about using the AGS at BNL. But AGS (having the polarized proton beam) has never built the intense antiproton source. Therefore we assume that these two schemes may be combined somewhere. For example, at AGS.

In this scheme we identify the following distinct parts:1. Slow extraction and transport of the primary proton beam of 26 GeV/c. We label it as the beam transport line-1(BTL-1).

2. After production target the beam transport line for antiprotons. We label it as BTL-2.

3. The antiproton accumulator AA.

4. Suggestion of the experiments for measuring the polarization transfer from

protons to antiprotonsat AGS

Parameters of the propane-diol polarized target :

C3H8O2

Density of frozen propane-diol (g/cm3) 1.1

Free hydrogen density(g/cm3) 0.12

Bound protons/free protons 4.2

Radiation length (cm) 45

Polarization build-up time (from zero to

0.8 of the maximum polarization) (min) 20

Target polarization, average during runs (%) 77

Target dimensions (cm) diameter: 2

length : 8.5

Effective hydrogen density (g/cm3) 0.085

Temperature (degree K) 0.48

Power dissipation (mW) 50

Microwave frequency (GHz) 70

[ J.C. Raoul, P. Autones, R. Auzolle, Apparatus for Simulations Measurements of the Polarization and Spin-Rotation Parametrs in High-Energy Elastic Scattering on Polarized Protons, Nuclear Instruments and Methods 125 (1975) 585-597 ]

Table 1.

Table 2.

[H. Grote, R. Hagedorn and J. Ranft, Atlas of Particle Spectra, CERN, Geneva, Switzerland, 1970.]

The yields of the negative particles in function of energy

The count rate per cycle and the time needed for accumulation of the scattering events for each energy

Conclusion

We are not aware of any paper devoted to the theoretical or experimental study of the spin

transfer mechanism from the polarized protons to the inclusively produced at zero degree

antiprotons.

Basing on the several experimental data on the spin-transfer effect in elastic and inclusive

reactions for protons and lambda hyperons we hope that similar effect may exist also for

antiprotons.

We would like to emphasize the importance to fulfill the special experiment for measuring

the polarization transfer tensor KLL in reaction

XpAp

at AGS. Initial proton beam with momentum around 22 GeV/c, longitudinal polarization 70%,

intensity 2·1011 p/cycle, may produces the longitudinally polarized pbar beam at zero degree.

Our estimates show that though such an experiment is difficult but it’s realizable.

Acknowledgements

We would like to thank for stimulating discussions and helps H. Artru, A. Efremov, Y. Makdisy, M. Ryskin, D. Sivers and H. Huang.

And I’m also thankful to the Organizing Committee and personally to prof. A. V. Efremov for invitation to this workshop.

Thank you!

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