Psi(2S) -> pi^+ pi^- J/psi Decay Distributions

TL;DR

This study analyzes the decay distributions of psi(2S) to pi+ pi- J/psi using BES data, revealing the presence of D-wave components in the dipion system and testing heavy quarkonium models.

Contribution

It provides the first detailed angular distribution analysis of psi(2S) decays, testing and constraining heavy quarkonium decay models including the Novikov-Shifman and Mannel-Yan models.

Findings

Dipion system requires D-wave and S-wave components.

The J/psi-(pi pi) system is consistent with pure S-wave.

The D-wave fraction decreases with increasing dipion mass.

Abstract

Using a sample of 3.8 M psi(2S) events accumulated with the BES detector, the process psi(2S) -> pi^+ pi^- 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, 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 should be present. We determine kappa = 0.183 +/- 0.002 +/- 0.003 based on the joint dipion mass - cos theta distribution. The fraction of D-wave as a function of the dipion mass is found to decrease with increasing dipion mass, in agreement with the model. We have also fit the Mannel-Yan model, another model that allows D-wave.