Pp phase shifts from psi '-> J/psi pi(+)pi(-) decays

The psi' -> J/psi pi(+)pi(-) decay process provides a new way to extract the pi pi S wave phase shifts up to 0.59GeV. In this paper we derive the formulae for extracting the pi pi S wave phase shifts from the invariant mass spectrum of pi pi in the psi' -> J/psi pi(+)pi(-) decay.