ψ(2S) → π+ π- J/ψ decay distributions -: art. no. 032002

Using a sample of 3.8 M psi(2S) events accumulated with the BES detector, the process psi(2S) --> pi(+) pi(r)-J/psi is studied. The angular distributions are compared with the general decay amplitude analysis of Cahn. We find that the dipion system requires some D wave amplitude, as well as S wave. On the other hand, the J/psi-(pi(+)pi(-)) relative angular momentum is consistent with being pure S wave. The decay distributions have been fit to heavy quarkonium models, including the Novikov-Shifman model. This model, which is written in terms of the parameter kappa, predicts that D wave pions should be present. We determine kappa = 0.183 +/- 0.002 +/- 0.003 based on the joint m(pi pi)-cos theta(pi)* distribution. The fraction of D wave amplitude as a function of m(pi pi) is found to decrease with increasing m(pi pi), in agreement with the model. We have also fit the Mannel-Yan model, which is another model that allows D wave pions.