Partial wave analysis of ψ′→π+π−π0 at BESII

Abstract The decay ψ ′ → π + π − π 0 is analyzed using a sample of 14 million ψ ′ events taken with the BESII detector at the BEPC, and the branching fraction is measured to be B ( ψ ′ → π + π − π 0 ) = ( 18.1 ± 1.8 ± 1.9 ) × 10 −5 . A partial wave analysis is carried out using the helicity amplitude method. ψ ′ → ρ ( 770 ) π is observed, and the branching fraction is measured to be B ( ψ ′ → ρ ( 770 ) π ) = ( 5.1 ± 0.7 ± 1.1 ) × 10 −5 , where the first error is statistical and the second one is systematic. A high mass enhancement with mass around 2.15 GeV / c 2 is also observed. Attributing this enhancement to the ρ ( 2150 ) resonance, the branching fraction is measured to be B ( ψ ′ → ρ ( 2150 ) π → π + π − π 0 ) = ( 19.4 ± 2.5 −3.4 +11.5 ) × 10 −5 . The results will help in the understanding of the longstanding “ ρπ puzzle” between J / ψ and ψ ′ hadronic decays.