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Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function ~(x, Q2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target. The data cover the kinematic range 0.023 < x < 0.6 and 1 (GeV/c) 2 < Q2 < 15 (GeV/c) 2. The integral fo~i0623 ~(x) dx evaluated at a fixed Qz of 2.5 (GeV/c) 2 is-0.0344-0.013(stat.)+0.005(syst.). Assuming Regge behavior at low x, the first moment F'~ = fl ~(x)dx is-0.037 ± 0.013(stat.)±0.005(syst.)±0.006(extrapol.

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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...