Proton-proton interactions with polarized internal targets in storage rings

Results of the first two experiments that use polarized hydrogen targets in proton storage rings are discussed. Both experiments used storage cell targets, i.e., long, narrow, windowless target cells into which polarized hydrogen atoms from an atomic-beam source are injected and through which the circulating beam passes. In the first experiment, carried out at the test storage ring of the Max Planck Institut in Heidelberg, a 27 MeV beam of alpha particles was passed through the target cell to measure the target polarization and the target thickness, and to investigate possible problems arising from background and from target depolarization by the beam. The target was used for a test of principle of the spin filter (spin-selective attenuation) as a means to polarize the circulating beam. The second experiment, currently in progress at the IUCF proton storage ring, has demonstrated the feasibility of spin correlation experiments at 200 MeV by detecting recoil protons in coincidence with scattered protons at forward angles. Both experiments used an improved atomic-beam source for polarized atoms and achieved target thicknesses of about 3x1013 polarized H/cm2 in a single hyperfine state of hydrogen