Elastic Scattering of Protons and Pions from Polarized HELIUM-3 at Intermediate Energies

A novel cryogenic technique has been used to produce polarized ^3He targets with a relative density of up to p = 12 atmospheres (or ~ 3 times 10^ {20} ^3He atoms/cm ^3; p = 1 atmosphere corresponds to 760 Torr or 101.3 kPa pressure at 273 K). In these targets the ^3He nuclei are polarized by spin exchange collisions with optically pumped rubidium atoms. From transmission measurements at wavelengths of 790-800 nm, pressure shifts, linewidths and lineshape asymmetries for the Rb 5S_{1/2} to 5P_{1/2} D1 transition have been determined. The Rb spin destruction rate was found to exhibit a quadratic increase versus ^3 He pressure: this might indicate the importance of Rb-^3He-^3He collision processes. The transmission results for circularly polarized light are well described by a model which predicts the dependence of the average Rb polarization on Rb density, ^3He pressure, light intensity and cell geometry. The Rb - ^3 He spin exchange cross section, < sigma_{Se^nu}> = 6.1 times 10^ {-20} cm^3s ^{-1}, was found to be independent of ^3He pressure up to p = 12.1 atmospheres. Maximum ^3He polarizations of up to 70% were achieved with cells of 35 cm ^3 volume containing ^3He at p = 7-10 atmospheres. This target has been used to measure cross sections and spin observables in elastic scattering of both pions and protons from polarized ^3He. Angular distributions of cross sections and the spin observables A_{OOON}, A_ {OONO}, and A_{OONN } have been measured for the elastic scattering of polarized protons from polarized ^3He at incident proton energies of 200, 290, 400 and 500 MeV. Measurements were made at 12 angles in the range 24^ circ-73^circ for most of the energies. The results are compared to two nonrelativistic microscopic momentum space optical model calculations. One calculation utilizes the Distorted Wave Impulse Approximation (DWIA) formalism whereas the second uses the Distorted Wave Born Approximation (DWBA). The overall agreement with the data is poor. For the target related spin observables (A_{OOON} and A_{OONN} the DWBA calculation represents a significant improvement over the DWIA model but the observables are poorly described whereas the beam related asymmetry (A_{OONO }) is well described. The measurement of elastic scattering of 100 MeV pi^+ from a polarized ^3He target is, together with recent measurements on the spin-1/2 nuclei ^{13}C and ^{15}N, the world's database for pion scattering from polarized spin-1/2 complex nuclei (A > 2). Measurements have been made at lab angles of 60^circ, 80^circ and 100^ circ, with the largest value A_ {y} = 0.89 +/- 0.12 occurring at 80^circ near a cross section minimum. This asymmetry is the largest observed to date in pion scattering from a spin-1 over 2 nucleus. The A_{y } data are qualitatively reproduced by a schematic model. However agreement with the data is significantly improved when realistic three-body Faddeev wave functions and a full nonlocal DWIA reaction model is used.