The decay mode ${\psi }^{\prime }\to \gamma \gamma \psi$ has been studied with the Mark-II detector at SPEAR. New measurements of branching ratios for decays of the type ${\psi }^{\prime }\to \gamma \chi$, $\chi \to \gamma \psi$ involving known $\chi$ states are presented. The existence of a $\chi$ state of mass near 3455 MeV/${\mathit{c}}^2$ produced in this decay chain is not confirmed, and the upper limit (90% confidence level) of the product of branching ratios is measured to be 0.13%. A new decay mode, ${\psi }^{\prime }\to {\pi }^0\psi$, which violates isospin conservation is observed with branching ratio (0.15±0.06)%.

• Received 28 January 1980

DOI:https://doi.org/10.1103/PhysRevLett.44.920