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

The decay ψ′→π+π−π0 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−π0)=(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/c2 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−π0)=(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.