Observation of a Doubly-strange Hyperon $\hat{I}ž(1720)$ in $J/\ddot{I}ˆ\to K^{-}\hat{I}{\pounds }^0\bar{\hat{I}}{ž}^{+}+c.c.$

Abstract

Based on a sample of $(10087\pm 44)\times 10^6$ $J/\ddot{I}ˆ$ events collected with the BESIII detector at BEPCII, we report the first observation of the decay $J/\ddot{I}ˆ\to K^{-}\hat{I}{\pounds }^0\bar{\hat{I}}{ž}^{+}+c.c.$. A partial wave analysis is performed to investigate the involved excited states. In addition to the well-established $\hat{I}ž(1690)$, a new doubly-strange hyperon $\hat{I}ž(1720)$ is observed decaying to $K^{-}\hat{I}{\pounds }^0$ with a mass of $1721.0\pm 5.2_{stat.}\pm 3.4_{syst.}\mathrm{MeV}/c^2$ and a width of $31.3\pm 18.3_{stat.}\pm 15.4_{syst.}\mathrm{MeV}$, with a statistical significance exceeding $10\ddot{I}ƒ$. The spin-parity hypothesis testing across various quantum number configurations reveals that the spin-parity of $\hat{I}ž(1720)$ favors $J^P={\frac{3}{2}}^{+}$. Furthermore, the branching fraction of $J/\ddot{I}ˆ\to K^{-}\hat{I}{\pounds }^0\bar{\hat{I}}{ž}^{+}+c.c.$ is determined to be $(2.68\pm 0.04_{stat.}\pm 0.17_{syst.})\times 10^{-5}$.

10 pages, 3 figures