Analyzing powers and cross sections of (p)over-right-arrowp→pnπ+ near threshold

Analyzing powers for (p) over right arrow-->pn pi(+) were measured for the first time close to threshold at beam energies that yield maximum pion momentum fractions (eta = p(c.m.)(max)/m(pi)c) Of eta = 0.22, 0.42, and 0.50, and enable a decomposition of the low order partial waves. Cross sections were measured at seven different beam energies with eta = 0.07, 0.17, 0.22, 0.28, 0.34, 0.42, and 0.50. The analysis shows that pion s-wave channels dominate the reaction. The p-wave channel containing the Delta resonance contributes, at eta = 0.22, less than one-tenth of the total cross section and less than one-third of the total cross section at eta = 0.42 and 0.50. The nonresonant p-wave channel contributes less than 1% of the cross section at these three energies.