Study of dalitz-plot distributions of the decays η→π+π-π0 and η→π+π-γ

Based on 80 884 events, we obtained the matrix element squared for the decay η→π+π-π0:|M (x,y)|2=1-(1.08±0.014)y+(0.03±0.03)y2+(0.05±0.03)x2 where x and y are the usual Dalitz-plot coordinates. The γ-ray energy spectrum was measured for 18 150 η→π+π-γ events. ρ dominance of the π+π- final state is strongly favored over a simple gauge-invariant matrix element.