Asymmetries for elastic scattering of ${\pi }^{\pm }$ from polarized ${}^3$He at $\Delta$ resonance energies

Asymmetries $A_y$ for ${\pi }^{+}$ and ${\pi }^{-}$ elastic scattering from polarized ${}^3$He were measured at incident energies passing through the $\pi$ nucleon $P_{33},$ or $\Delta$(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 ${\pi }^{+}$ scattering near $50°$–60$°$, which cannot be reproduced by multiple scattering theory and Faddeev wave functions. A hybrid model, which adds a $\Delta$-neutron spin-spin interaction term to the conventional calculations, provides a good description of the ${\pi }^{+}$ data. For ${\pi }^{-}$ scattering this term predicts a negligible effect on $A_y$ and the data do not show the anomalous $A_y$ seen with ${\pi }^{+}$.