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-π0 and η′→π+π-e+e-, measuring absolute branching fractions (37-9+11±4)×10-4 and (25-9+12±5)×10-4, respectively. For η′→π+π-π0, this result probes the mechanism of isospin violation and the roles of π0/η/η′-mixing and final state rescattering in strong decays. We also set upper limits on branching fractions for η′ decays to π+π-μ+μ-, 2(π+π-), π+π-2π0, 2(π+π-)π0, 3(π+π-), and invisible final states. © 2009 The American Physical Society.