Partial-wave analysis ofJ/ψ→γηπ+π−

We present a study of the decay J/ψ→γη${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{\mathrm{-}}$ using the Mark III detector at the SLAC ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ storage ring SPEAR. A partial-wave amplitude analysis is performed on the η${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{\mathrm{-}}$ system in the mass region from 1.2 to 1.5 GeV. We observe two η${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{\mathrm{-}}$ resonances, each decaying via ${\mathit{a}}_0$(980)π. We identify one as the axial-vector meson ${\mathit{f}}_1$(1285) and the other as a pseudoscalar resonance at 1.40 GeV.