The pi pi Phase Shifts from psi' to J/psi pi^+ pi^- Decays

Abstract

The $ψ'\to J/ψπ^+π^-$ decay process provides a new way to extract the $ππ$ $S$ wave phase shifts up to $0.59GeV$. In this paper we derive the formulae for extracting the $ππ$ $S$ wave phase shifts from the invariant mass spectrum of $ππ$ in the $ψ'\to J/ψπ^+π^-$ decay.