Observation of an Axial-Vector State in the Study of the Decay ψ(3686)→ϕηη^{'}.

Using (2712.4±14.3)×10^{6} ψ(3686) events collected with the BESIII detector at BEPCII, a partial wave analysis of the decay ψ(3686)→ϕηη^{'} is performed with the covariant tensor approach. In addition to the established states h_{1}(1900) and ϕ(2170), an axial-vector state with a mass near 2.3  GeV/c^{2} is observed for the first time. Its mass and width are measured to be 2316±9_{stat}±30_{syst}  MeV/c^{2} and 89±15_{stat}±26_{syst}  MeV, respectively. The product branching fractions of B[ψ(3686)→X(2300)η^{'}]B[X(2300)→ϕη] and B[ψ(3686)→X(2300)η]B[X(2300)→ϕη^{'}] are determined to be (4.8±1.3_{stat}±0.7_{syst})×10^{-6} and (2.2±0.7_{stat}±0.7_{syst})×10^{-6}, respectively. The branching fraction B[ψ(3686)→ϕηη^{'}] is measured for the first time to be (3.14±0.17_{stat}±0.24_{syst})×10^{-5}. The first uncertainties are statistical and the second are systematic.