Understanding the Possible Proton Antiproton Bound State Observed by BES Collaboration

Abstract

We comment on the quantum numbers and decay channels of the possible proton antiproton bound state observed by BES Collaboration. Based on the general symmetry consideration and available experimental information, we conclude that the quantum number of this state is very likely to be $J^{PC}=0^{-+}, I^G=0^+$, which can not decay into final states $\pi^+\pi^-, 2\pi^0, K{\bar K}, 3\pi$. Besides its dissociation into $p\bar p$, the other important mesonic decay modes could be $\eta \pi\pi$, $\eta'\pi\pi$, $\eta\eta\eta$, $4\pi$, $K{\bar K}\pi$, $\eta K{\bar K}$, $K\bar K \pi\pi$, 6$\pi$. Experimental search of this signal in these meson final states is strongly called for.