The proton analyzing power $A_y$ in the pion production reaction $\overrightarrow{p}d\to {\pi }^0{}^3\mathrm{He}$ has been calculated including one- and two-body meson production mechanisms with a proper treatment of the three-nucleon dynamics and an accurate solution of the 3N bound-state problem for phenomenological two-nucleon potentials. In the region around the Δ resonance, the structure of the analyzing power can be understood once interference effects among amplitudes describing intermediate $\Delta N$ formation in different orbital states are considered along with the additional interference with the S-wave pion-production amplitudes. Then, the inclusion of three-nucleon dynamics in the initial state produces the structure of the analyzing power that has been observed experimentally.

• Received 23 July 2004

DOI:https://doi.org/10.1103/PhysRevC.71.041001