Observation and study of the decay $J/\ddot{I}ˆ\to \ddot{I}•\hat{I}\cdot \hat{I}{\cdot }^{\prime }$

Abstract

We report the observation and study of the decay $J/\ddot{I}ˆ\to \ddot{I}•\hat{I}\cdot \hat{I}{\cdot }^{\prime }$ using $1.3\times 10^9$ $J/\ddot{I}ˆ$ events collected with the BESIII detector. Its branching fraction, including all possible intermediate states, is measured to be $(2.32\pm 0.06\pm 0.16)\times 10^{-4}$. We also report evidence for a structure, denoted as $X$, in the $\ddot{I}•\hat{I}{\cdot }^{\prime }$ mass spectrum in the $2.0-2.1$ GeV/$c^2$ region. Using two decay modes of the $\hat{I}{\cdot }^{\prime }$ meson (${\hat{I}}^3\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ and $\hat{I}\cdot \ddot{I}{€}^{+}\ddot{I}{€}^{-}$), a simultaneous fit to the $\ddot{I}•\hat{I}{\cdot }^{\prime }$ mass spectra is performed. Assuming the quantum numbers of the $X$ to be $J^P=1^{-}$, its significance is found to be 4.4$\ddot{I}ƒ$, with a mass and width of $(2002.1\pm 27.5\pm 21.4)$ MeV/$c^2$ and $(129\pm 17\pm 9)$ MeV, respectively, and a product branching fraction $\mathcal{B}(J/\ddot{I}ˆ\to \hat{I}\cdot X)\times \mathcal{B}(X\to \ddot{I}•\hat{I}{\cdot }^{\prime })=(9.8\pm 1.2\pm 1.7)\times 10^{-5}$. Alternatively, assuming $J^P=1^{+}$, the significance is 3.8$\ddot{I}ƒ$, with a mass and width of $(2062.8\pm 13.1\pm 7.2)$ MeV/$c^2$ and $(177\pm 36\pm 35)$ MeV, respectively, and a product branching fraction $\mathcal{B}(J/\ddot{I}ˆ\to \hat{I}\cdot X)\times \mathcal{B}(X\to \ddot{I}•\hat{I}{\cdot }^{\prime })=(9.6\pm 1.4\pm 2.0)\times 10^{-5}$. The angular distribution of $J/\ddot{I}ˆ\to \hat{I}\cdot X$ is studied and the two $J^P$ assumptions of the $X$ cannot be clearly distinguished due to the limited statistics. In all measurements the first uncertainties are statistical and the second systematic.

10 pages, 6 figures and 4 tables