We report the observation of a large asymmetry in the elastic scattering of 100 MeV ${\mathrm{\pi }}^{+}$ from a polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ target. Measurements have been made at laboratory angles of 60°, 80°, and 100°, with the largest value ${\mathit{A}}_{\mathit{y}}$=0.89±0.12 occurring at 80°, near a cross-section minimum. This asymmetry is the largest observed to date in pion scattering from a spin-1/2 nucleus. The ${\mathit{A}}_{\mathit{y}}$ 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 distorted-wave impulse approximation reaction model are used.

• Received 3 September 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.3356