Observation of η′ decays to π+π-π0 and π+π-e+e-

Using ψ(2S) → π + π - J/ψ, J/ψ → γη' events acquired with the CLEO-c detector at the CESR e + e - collider, we make the first observations of the decays η' → π + π - π 0 and η' → π + π - e + e - , measuring absolute branching fractions(37 +11 -9 ± 4) X 10-4 and (25 +12 -9 ± 5) × 10 -4 , respectively. For 77' → π + π - π 0 , this result probes the mechanism of isospinviolation and the roles of π 0 /η/η'-mixing and final state rescattering in strong decays. We also set upper limits on branching fractionsfor η' decays to π + π - μ + μ - , 2(π + π - ), π + π - 2π 0 , 2(π + π - )π 0 , 3(π + π - ), and invisible final states.