Event generator for ψ′ decays of VP and PP modes

A convenient generator, based on the existing framework of BES simulation, applicable generally to both ψ′ and J/ψ decays of VP and PP modes, is established. The corresponding angular distribution is taken into account. A similar generator is also established for the successive J/ψ decay in the process of ψ′→X + J/ψ. In the measurement of branching ratios for ψ′→γη, γη′, ωπ0, π+π-, K+K-, this generator is used to determine the selection efficiency and estimate the background.