First observation of the isospin violating decay $J/\ddot{I}ˆ\to \hat{I}›\bar{\hat{I}}{\pounds }^0+c.c.$

Abstract

Using a sample of $(225.2\pm 2.8)\times 10^6$ $J/\ddot{I}ˆ$ events collected with the BESIII detector, we present results of a study of $J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}›\bar{\hat{I}}›$ and report the first observation of the isospin violating decay $J/\ddot{I}ˆ\to \hat{I}›\bar{\hat{I}}{\pounds }^0+c.c.$, in which $\bar{\hat{I}}{\pounds }^0$ decays to ${\hat{I}}^3\bar{\hat{I}}›$. The measured branching fractions are $\mathcal{B}(J/\ddot{I}ˆ\to \bar{\hat{I}}›\hat{I}{\pounds }^0$) = $(1.46\pm 0.11\pm 0.12)\times 10^{-5}$ and $\mathcal{B}(J/\ddot{I}ˆ\to \hat{I}›\overline{\hat{I}{\pounds }^0}$) = $(1.37\pm 0.12\pm 0.11)\times 10^{-5}$. We search for $\hat{I}›(1520)\to {\hat{I}}^3\hat{I}›$ decay, and find no evident signal, and an upper limit for the product branching fraction $\mathcal{B}(J/\ddot{I}ˆ\to \hat{I}›\bar{\hat{I}}›(1520)+c.c.)\times \mathcal{B}(\hat{I}›(1520)\to {\hat{I}}^3\hat{I}›)<4.1\times 10^{-6}$ is set at the 90% confidence level. We also report the observation of $\hat{I}{\cdot }_c\to \hat{I}›\bar{\hat{I}}›$ in $J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}{\cdot }_c$, $\hat{I}{\cdot }_c\to \hat{I}›\bar{\hat{I}}›$ and measure the branching fraction $\mathcal{B}(\hat{I}{\cdot }_c\to \hat{I}›\bar{\hat{I}}›)=(1.16\pm 0.12(stat)\pm 0.19(syst)\pm 0.28(PDG))\times 10^{-3}$.

9 pages, 6 figures; This is a publication-version at Phys. Rev. D