Measurement of the branching fractions for $J/\psi\to\gamma\pi^0$, $\gamma\eta$ and $\gamma\eta^{\prime}$

TL;DR

This paper measures the branching fractions of specific radiative decays of the J/psi particle, providing precise experimental data and insights into the eta-eta' mixing angle.

Contribution

First precise measurement of branching fractions for J/psi decays into gamma pi0, eta, and eta', and determination of the eta-eta' mixing angle.

Findings

Branching fraction for J/psi to gamma pi0: (3.13^{+0.65}_{-0.44})×10^{-5}

Branching fraction for J/psi to gamma eta: (11.23±0.89)×10^{-4}

Branching fraction for J/psi to gamma eta': (5.55±0.44)×10^{-3}

Abstract

The decay modes $\jpsi\ar\gamma\pi^0, \gamma\eta$ and $\gamma\etap$ are analyzed using a data sample of 58 million $\jpsi$ decays collected with the BESII detector at BEPC. The branching fractions are determined to be: $Br(\jpsi\ar\gamma\pi^0)=(3.13^{+0.65}_{-0.44})\times10^{-5}$, $Br(\jpsi\ar\gamma\eta)=(11.23\pm0.89)\times10^{-4}$, and $Br(\jpsi\ar\gamma\etap)=(5.55\pm0.44)\times10^{-3}$, where the errors are combined statistical and systematic errors. The ratio of partial widths $\Gamma(\jpsi\ar\gamma\etap)/\Gamma(\jpsi\ar\gamma\eta)$ is measured to be $4.94\pm0.40$, and the singlet-octet pseudoscalar mixing angle of $\eta-\etap$ system is determined to be $\theta_{P}=(-22.08\pm0.81)^{\circ}$.