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A feasibility test of a new method to polarize beams of strongly interacting charged particles circulating in a storage ring is described. The stored particles, here protons, pass through a polarized hydrogen gas target (thickness 6 x 10 13 H/cm 2 ) in the ring some 10 10 times and become partially polarized because one spin state is attenuated faster than the other. The polarization buildup is clearly demonstrated in the present experiment PACS numbers: 29.27.Hj, 29.20.DhThe study of current problems in nuclear and in elementary particle physics often requires the use of spinpolarized projectiles. Polarized protons and polarized neutrons were produced for the first time some 40 years ago in experiments in which an unpolarized target was bombarded with an unpolarized beam [1]. For a number of different reactions, the particles emitted at angles 0^0° were found to be partially polarized. The polarization of the particles was detected as a left-right asymmetry in a second scattering or reaction which served as the polarization analyzer (double scattering).A major difficulty in this method to produce polarized particle beams is the large loss in intensity and the large spread in angle and energy introduced by nuclear scattering from a target. For beams of protons and deuterons, these problems have been overcome by the development of sources of polarized ions, i.e., the preparation of polarized atoms by atomic methods (e.g., Stern-Gerlach separation) and subsequent ionization of the atoms to produce polarized ions [2].Here we report the first feasibility test of a new method to polarize beams of strongly interacting charged particles. The method is of particular interest for the production of polarized antiprotons, for which the construction of polarized ion sources is not feasible, and for which the large loss in intensity resulting from the double-scattering method has so far prevented experiments with beams of polarized antiprotons.The method can be described as spin-selective attenuation of the particles circulating in a storage ring. The idea was first proposed by Csonka [3]: a polarized target-in our case a target of polarized hydrogen gas (t)-is in-serted in a storage ring. The particles stored in the ring pass through the target for a sufficiently long time that a fraction of the particles is lost by nuclear scattering in the target. Since in general the total strong interaction cross section is different for beam and target spins parallel (IT) an d antiparallel (|j), one spin direction of the circulating beam is depleted more than the other, so that the circulating beam becomes increasingly polarized, while the intensity of the beam decreases with time. The method has been referred to as a "spin filter" since the spin-selective attenuation amounts to a filter which is more transparent to one spin state of the beam than the other.For simplicity, we assume that the target has polarization PT in the vertical direction, i.e., normal to the orbit of the ions in the storage ring. The beam can be considered to cons...

A target of gaseous polarized hydrogen was formed by injecting polarized hydrogen atoms (produced by Stern–Gerlach spin separation) into a storage cell consisting of a cylindrical tube open at both ends. The target was placed in a storage ring to study the target characteristics (nuclear polarization, target thickness, radiation resistance). A weak transverse guide field (5 G) was applied to define the polarization direction. When atoms in a single hyperfine state were selected, the nuclear polarization of the target was measured to be 0.80±0.02. The areal density of the target under these conditions was (5.5±0.2)×1013 H/cm2, while for two spin states (applicable to experiments in high energy rings where a strong magnetic field can be applied to the target) the target thickness was found to be (8.2±0.3)×1013 H/cm2. The target polarization was unaffected by prolonged exposure of the target to beams up to 1 mA.