Measurement of the branching fractions for $J/\psi\to\gamma\pi^0$,   $\gamma\eta$ and $\gamma\eta^{\prime}$
  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 $\theta_{P}=(-22.08\pm0.81)^{\circ}$. 
M. Ablikim, J. Z. Bai, et al, BES Collaboration