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We report here a measurement of the analyzing power Ay in 185 MeV elastic proton-proton (pp) scattering at forward angles (2.5°–10.5° in the laboratory). In this angular range the Coulomb and nuclear amplitudes are of similar magnitude and measurements of polarization observables allow separation of the real and imaginary components of the nuclear amplitudes by their interference with the known Coulomb amplitude.[1] Precise measurements at such small angles can be difficult due to the presence of beam halo or scattering from target materials other than hydrogen. In the present experiment we have used both a windowless gas jet target and coincident detection of the low energy proton at large angles to eliminate these backgrounds.

The polarization transfer in p-d elastic scattering was shown to be sensitive to the details of the tensor force in the N-N interaction. Therefore measurements of the polarization transfer coefficients in this scattering have been carried out at an incident proton energy of 22.7 MeV. The data are compared to rigorous Faddeev calculations using different N-N potentials. The observable most sensitive to details of the potentials is the nucleon-nucleon polarization transfer coefficient K y y′ (Wolfenstein’s depolarization parameter D). The agreement of the K y y′ data with the calculations using the Bonn A potential is much better than with the Paris or Bonn B potentials. Results of recent measurements of K z x′ are presented and compared to the calculations. Measurements of the polarization transfer to the recoil deuterons are in progress.

A cylindrically symmetric detector system has been installed in one of the straight sections of the Indiana Cooler. The apparatus is suitable for measuring the polarization of 80–300 MeV stored proton beams. Fig. 1 shows a schematic view of the detector array consisting of a 1.5 mm thick scintillator (F), 2 wire chambers, a 102 mm thick scintillator (E) and a 6.5 mm thick scintillator (V). The detector system was designed for the first nuclear physics experiment (p+p → p+p+π° near threashold [1]) at the Indiana Cooler and accepts scattering angles between \( \vartheta _1 = 5^\circ {\text{ and }}\vartheta _2 = 20^\circ \) with respect to the beam axis.

Based on our experience with the Indiana Cooler storage ring some aspects relevant to the design of internal polarized gas target experiments are discussed. In particular, it is pointed out that, perhaps contrary to general perception, increasing the target thickness does not necessarily lead to a proportional gain in luminosity: In our studies with cooled beams of 100 to 200 MeV, interacting with internal H2 targets, the luminosity as a function of target thickness shows a broad maximum in the range of 1014 to 1015 atoms/cm2.