Asymmetries for elastic scattering ofπ±from polarized3He atΔresonance energies

Abstract

Asymmetries ${A}_{y}$ for ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ elastic scattering from polarized ${}^{3}$He were measured at incident energies passing through the $\ensuremath{\pi}$ nucleon ${P}_{33},$ or $\ensuremath{\Delta}$(1232), resonance. The data were taken at the Clinton P. Anderson Meson Physics Facility using the high-energy pion channel ${P}^{3}$ and a large acceptance spectrometer to detect the scattered pions. The polarized ${}^{3}$He target, originally developed at TRIUMF, was modified for these experiments by the addition of diode lasers. Completely unexpected negative asymmetries were observed at and below the resonance in ${\ensuremath{\pi}}^{+}$ scattering near $50\ifmmode^\circ\else\textdegree\fi{}$--60$\ifmmode^\circ\else\textdegree\fi{}$, which cannot be reproduced by multiple scattering theory and Faddeev wave functions. A hybrid model, which adds a $\ensuremath{\Delta}$-neutron spin-spin interaction term to the conventional calculations, provides a good description of the ${\ensuremath{\pi}}^{+}$ data. For ${\ensuremath{\pi}}^{\ensuremath{-}}$ scattering this term predicts a negligible effect on ${A}_{y}$ and the data do not show the anomalous ${A}_{y}$ seen with ${\ensuremath{\pi}}^{+}$.