Observation of an axial-vector state in the study of $\ddot{I}ˆ(3686)\to \ddot{I}•\hat{I}\cdot \hat{I}{\cdot }^{\prime }$ decay

Abstract

Using (2712.4 $\pm$ 14.3)$\times 10^6$ $\ddot{I}ˆ(3686)$ events collected with the BESIII detector at BEPCII, a partial wave analysis of the decay $\ddot{I}ˆ(3686)\to \ddot{I}•\hat{I}\cdot \hat{I}{\cdot }^{\prime }$ is performed with the covariant tensor approach. An axial-vector state with a mass near 2.3 $GeV/{\mathrm{c}}^2$ is observed for the first time. Its mass and width are measured to be 2316 $\pm 9_{\mathrm{stat}}\pm 30_{\mathrm{syst}}MeV/{\mathrm{c}}^2$ and 89 $\pm 15_{\mathrm{stat}}\pm 26_{\mathrm{syst}}\mathrm{MeV}$, respectively. The product branching fractions of $\mathcal{B}(\ddot{I}ˆ(3686)\to X(2300)\hat{I}{\cdot }^{\prime })\mathcal{B}(X(2300)\to \ddot{I}•\hat{I}\cdot )$ and $\mathcal{B}(\ddot{I}ˆ(3686)\to X(2300)\hat{I}\cdot )\mathcal{B}(X(2300)\to \ddot{I}•\hat{I}{\cdot }^{\prime })$ are determined to be (4.8 $\pm 1.3_{\mathrm{stat}}\pm 0.7_{\mathrm{syst}})\times 10^{-6}$ and (2.2 $\pm 0.7_{\mathrm{stat}}\pm 0.7_{\mathrm{syst}})\times 10^{-6}$, respectively. The branching fraction $\mathcal{B}(\ddot{I}ˆ(3686)\to \ddot{I}•\hat{I}\cdot \hat{I}{\cdot }^{\prime })$ is measured for the first time to be (3.14$\pm 0.17_{\mathrm{stat}}\pm 0.24_{\mathrm{syst}})\times 10^{-5}$. The first uncertainties are statistical and the second are systematic.