Analyzing powers in p→p→pnπ+ and determination of pion S and P wave amplitudes near threshold

Analyzing powers were measured and used to quantify the observation that s-wave processes dominate near threshold. Values of Ay(θπ,φπ=0°) are presented for η values of 0.22, 0.42 and 0.50. Maximum analyzing powers AN0 are equal to −0.13, −0.24, and −0.28, respectively. A partial wave analysis, made possible by the new analyzing powers and available cross sections, indicates that the s-wave contribution to the cross section constitutes about 91% of the total cross section at η=0.22, or 300 MeV. It decreases to about 75% for η=0.5.