Unbroken chiral symmetry (with a vanishing $\sigma$ term) relates the ${\psi }^{\prime }\to \psi \pi \pi$ decay amplitude to three basic parameters. Two of these parameters put strong angular correlations in the amplitude which, apparently, are not observed. Taking these two parameters to vanish, we obtain an isotropic decay which is strongly peaked in the region where the invariant mass of the $\pi \pi$ system is large.

• Received 23 April 1975

DOI:https://doi.org/10.1103/PhysRevLett.35.1