Study of <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo>→</mo><mi>η</mi><mi>ϕ</mi></math> via initial state radiation at Belle

Using 980 fb−1 of data collected on and around the ϒ(nS) (n=1, 2, 3, 4, 5) resonances with the Belle detector at the KEKB collider, we measure the cross section of e+e−→ηϕ from threshold to 3.95 GeV via initial state radiation. There are clear ϕ(1680) and J/ψ signals but no significant ϕ(2170) signal in the ηϕ final state. The branching fraction B[J/ψ→ηϕ] is measured to be (7.2&#177;0.8&#177;0.5)&#215;10−4. The resonant parameters of ϕ(1680) are determined to be mϕ(1680)=(1696&#177;8&#177;10) MeV/c2 (statistical and systematic errors, respectively), Γϕ(1680)=(175&#177;13&#177;16) MeV and, depending on the possible presence of predominantly constructive or destructive interference between ϕ(1680) and continuum production, Γϕ(1680)e+e−&#183;B[ϕ(1680)→ηϕ] and B[ϕ(1680)→ηϕ] are determined to be (75&#177;10&#177;11) eV and (25&#177;12&#177;2)% or (207&#177;16&#177;20) eV and (23&#177;10&#177;2)%, respectively. The upper limit for Γϕ(2170)e+e−&#183;B[ϕ(2170)→ηϕ] is determined to be either 0.17 or 18.6 eV at the 90% confidence level.