Implications of a DK molecule at 2.32 GeV

Abstract

We discuss the implications of a possible quasinuclear DK bound state at 2.32 GeV. Evidence for such a state was recently reported in ${D}_{s}^{+}{\ensuremath{\pi}}^{0}$ by the BaBar Collaboration. We first note that a conventional quark model $c\overline{s}$ assignment is implausible, and then consider other options involving multiquark systems. An $I=0$ $c\overline{s}n\mathrm{n\ifmmode \bar{}\else \={}\fi{}}$ baryonium assignment is one possibility. We instead favor a DK meson molecule assignment, which can account for the mass and quantum numbers of this state. The higher-mass scalar $c\overline{s}$ state expected at 2.48 GeV is predicted to have a very large DK coupling, which would encourage formation of an $I=0$ DK molecule. Isospin mixing is expected in hadron molecules, and a dominantly $I=0$ DK state with some $I=1$ admixture could explain both the narrow total width of the 2.32 GeV state as well as the observed decay to ${D}_{s}^{+}{\ensuremath{\pi}}^{0}.$ Additional measurements that can be used to test this and related scenarios are discussed.