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The PAX Collaboration has successfully performed a spin-filtering experiment with protons at the COSY-ring. The measurement allowed the determination of the spin-dependent polarizing cross section, that compares well with the theoretical prediction from the nucleon-nucleon potential. The test confirms that spin-filtering can be adopted as a method to polarize a stored beam and that the present interpretation of the mechanism in terms of the proton-proton interaction is correct. The outcome of the experiment is of utmost importance in view of the possible application of the method to polarize a beam of stored antiprotons.

QC 20121212

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The paper describes the commissioning of the experimental equipment and the machine studies required for the first spin-filtering experiment with protons at a beam kinetic energy of 49.3MeV in COSY. The implementation of a low-β insertion made it possible to achieve beam lifetimes of τb=8000s in the presence of a dense polarized hydrogen storage-cell target of areal density dt=(5.5±0.2)×1013atoms/cm2. The developed techniques can be directly applied to antiproton machines and allow for the determination of the spin-dependent p¯p cross sections via spin filtering