Branching Fractions for $\psi(2S) to \gamma \eta'$ and $\gamma \eta$

TL;DR

This paper reports the first measurements of specific radiative decay branching fractions of the $(2S)$ particle to $'$ and $$, and uses these to explore meson mixing angles.

Contribution

It provides the first experimental measurements of these branching fractions and uses them to determine the pseudoscalar meson mixing angle.

Findings

Branching fraction for $(2S) '$ decay is approximately 1.54 x 10^{-4}.

Branching fraction for $(2S) $ decay is approximately 0.53 x 10^{-4}.

Results support models involving $'-$ mixing.

Abstract

We report the first measurements of the branching fractions: $B(\psi(2S) -> \gamma \eta') = (1.54 \pm 0.31 \pm 0.23) x 10^{-4}$ and $B(\psi(2S) -> \gamma \eta) = (0.53 \pm 0.31 \pm 0.08) x 10^{-4}$. The $\psi(2S)$ to $\gamma \eta'$ result is consistent with expectations of a model that considers the possibility of $\eta' - \eta$ mixing. The ratio of the $\psi(2S)$ to $\gamma \eta'$ and $\psi(2S)$ to $\gamma \eta$ rates is used to determine the pseudoscalar octet-singlet mixing angle.