Measurement of the branching fractions forJ/ψ→γπ0,γηandγη′

The decay modes J/{psi}{yields}{gamma}{pi}{sup 0}, {gamma}{eta} and {gamma}{eta}{sup '} are analyzed using a data sample of 58x10{sup 6} J/{psi} decays collected with the BESII detector at the BEPC. The branching fractions are determined to be: Br(J/{psi}{yields}{gamma}{pi}{sup 0})=(3.13{sub -0.47}{sup +0.65})x10{sup -5}, Br(J/{psi}{yields}{gamma}{eta})=(11.23{+-}0.89)x10{sup -4}, and Br(J/{psi}{yields}{gamma}{eta}{sup '})=(5.55{+-}0.44)x10{sup -3}, where the errors are combined statistical and systematic errors. The ratio of partial widths {gamma}(J/{psi}{yields}{gamma}{eta}{sup '})/{gamma}(J/{psi}{yields}{gamma}{eta}) is measured to be 4.94{+-}0.40, and the singlet-octet pseudoscalar mixing angle of {eta}-{eta}{sup '} system is determined.