Date of Original Version
Abstract or Table of Contents
We measure the mass of the η′ meson using ψ(2S)→π+π-J/ψ, J/ψ→γη′ events acquired with the CLEO-c detector operating at the CESR e+e- collider. Using three decay modes, η′→ρ0γ, η′→π+π-η with η→γγ, and η′→π+π-η with η→π+π-π0, we find Mη′=957.793±0.054±0.036 MeV, in which the uncertainties are statistical and systematic, respectively. This result is consistent with but substantially more precise than the current world average.