Search for rare and forbidden η′ decays

We have searched for rare and forbidden decays of the η′ meson in hadronic events at the CLEO II detector. The search is conducted on 4.80 fb⁻¹ of e⁺e⁻ collisions at 10.6 GeV center-of-mass energy at the Cornell Electron Storage Ring. We find no signals and set 90% confidence level upper limits of their branching fractions: B(η′→e⁺e⁻η)<2.4×10⁻³, B(η′→e⁺e⁻π⁰)<1.4×10⁻³, B(η′→e⁺e⁻γ)<0.9×10⁻³, and B(η′→eμ)<4.7×10⁻⁴. We also fit the matrix element of the η′→π⁺π⁻η Dalitz plot with the parametrization |M|²=A|1+αy|², where y is a linear function of the kinetic energy of the ηand find Re (α)=−0.021±0.025.