Thanks guys. The BF's are actually not 50/50 but 52/48. Why should they be slightly different? Does the fact that alpha for p pi0 (36 deg) and for n pi+ (167 deg) relevant for this? Appreciate your comments.
Can someone describe the Feynman diagram for the Sigma plus decay to a positive pion and a neutron? I'm fine with the primary decay to the neutral pion and a proton. There appears to be insufficient down quarks created.