Some properties of the newly observed X(1835) state at BES

Abstract

Recently the BES collaboration has announced observation of a resonant state in the ${\pi }^{+}{\pi }^{-}{\eta }^{\prime }$ spectrum in $J/\psi \to \gamma {\pi }^{+}{\pi }^{-}{\eta }^{\prime }$ decay. Fitting the data with a $0^{-+}$ state, the mass is determined to be 1833.7 MeV with $7.7\sigma$ statistic significance. This state is consistent with the one extracted from previously reported $p\bar{p}$ threshold enhancement data in $J/\psi \to \gamma p\bar{p}$. We study the properties of this state using QCD anomaly and QCD sum rules assuming X(1835) to be a pseudoscalar and show that it is consistent with data. We find that this state has a sizeable matrix element $<0|G\tilde{G}|G_p>$ leading to branching ratios of $(2.61\sim 7.37)\times 10^{-3}$ and $(2.21\sim 10.61)\times 10^{-2}$ for $J/\psi \to \gamma G_p$ and for $G_p\to {\pi }^{+}{\pi }^{-}{\eta }^{\prime }$, respectively. Combining the calculated branching ratio of $J/\psi \to \gamma G_p$ and data on threshold enhancement in $J/\psi \to \gamma p\bar{p}$, we determine the coupling for $G_p-p-\bar{p}$ interaction. We finally study branching ratios of other $J/\psi \to \gamma +threemesons$ decay modes. We find that $J/\psi \to \gamma G_p\to \gamma ({\pi }^{+}{\pi }^{-}\eta ,KK{\pi }^0)$ can provide useful tests for the mechanism proposed.

Comments: 13 pages, 3 figures. The final version to appear at EPJC