Angular distributions of the differential cross section and the analyzing power for ground state transitions in the ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},{\pi }^{+}){}_{}{}^{4,5}{}_{}{}^{}\mathrm{He}$ reactions have been measured at 800 MeV using a polarized proton beam. The angular distributions of the analyzing power $A_y$ reveal a surprisingly strong spin dependence in these reactions. The analyzing power from the ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},{\pi }^{+}){}_{}{}^4{}_{}{}^{}\mathrm{He}$ reaction is compared with $A_y$ data from elastic p-He scattering, the $\mathrm{pp}\to \mathrm{d}\pi$ reaction, and pion nucleon scattering, in order to find an indication of the origin to the spin dependence. Reasonably good agreement is obtained with the pion-nucleon $A_y$ data when momentum sharing is assumed between the nuclear vertices involved in a pion rescattering diagram of the ($\mathrm{p},\pi$) reaction.

[NUCLEAR REACTIONS ${}_{}{}^3{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},{\pi }^{+}){}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},{\pi }^{+}){}_{}{}^5{}_{}{}^{}\mathrm{He}$, $E_x=0\mathrm{}$ MeV, $T_{\mathrm{p}}=800\mathrm{}$ MeV; measured $\sigma (E,\theta )$, $A_y$ from ${\theta }_{\pi }^{\mathrm{c}.\mathrm{m}.\mathrm{}}=10\mathrm{}° \mathrm{to} 80°$. Comparisons with $A_y$ from ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}(\overrightarrow{\mathrm{p}},\mathrm{p}){}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}$, $\overrightarrow{\mathrm{p}}\mathrm{p}\to \mathrm{d}\pi$, and $\pi \overrightarrow{\mathrm{p}}$.]

• Received 12 September 1983

DOI:https://doi.org/10.1103/PhysRevC.29.553