Branching Fractions for $\psi (2S)to\gamma {\eta }^{\prime }$ and $\gamma \eta$

Abstract

We report the first measurements of the branching fractions: $B(\psi (2S)->\gamma {\eta }^{\prime })=(1.54\pm 0.31\pm 0.23)x10^{-4}$ and $B(\psi (2S)->\gamma \eta )=(0.53\pm 0.31\pm 0.08)x10^{-4}$. The $\psi (2S)$ to $\gamma {\eta }^{\prime }$ result is consistent with expectations of a model that considers the possibility of ${\eta }^{\prime }-\eta$ mixing. The ratio of the $\psi (2S)$ to $\gamma {\eta }^{\prime }$ and $\psi (2S)$ to $\gamma \eta$ rates is used to determine the pseudoscalar octet-singlet mixing angle.

10 pages with 3 figures