Observation of ψ(4040) and ψ(4160) decay into ηj/ψ

The cross section for e⁺e^-→ηJ/ψ between √s=3.8 GeV and 5.3 GeV is measured via initial state radiation using 980 fb^-1 of data on and around the Υ(nS)(n=1,2,3,4,5) resonances collected with the Belle detector at KEKB. Two resonant structures at the ψ(4040) and ψ(4160) are observed in the ηJ/ψ invariant mass distribution. Fitting the mass spectrum with the coherent sum of two Breit-Wigner functions, one obtains B(ψ(4040)→ηJ/ψ) ·Γe⁺e^-ψ(4040)=(4.8±0.9±1.5) eV and B(ψ(4160)→ηJ/ψ)·Γe⁺e ^-ψ(4160)=(4.0±0.8±1.4) eV for one solution and B(ψ(4040)→ηJ/ψ)·Γe⁺e ^-ψ(4040)=(11.2±1.3±2.1) eV and B(ψ(4160) →ηJ/ψ)·Γe⁺e^-ψ(4160)=(13. 8±1.3±2.1) eV for the other solution, where the first errors are statistical and the second are systematic. This is the first measurement of this hadronic transition mode of these two states, and the partial widths to ηJ/ψ are found to be about 1 MeV. There is no evidence for the Y(4260), Y(4360), ψ(4415), or Y(4660) in the ηJ/ψ final state, and upper limits of their production rates in e⁺e^- annihilation are determined.