We analyze recent data from the BABAR and Belle Collaborations on the $X(3872)$ resonance in the $J/\psi {\pi }^{+}{\pi }^{-}$ and $D^0{\overline{D}}^0{\pi }^0$ decay channels, taking careful account of the universal features of an $S$-wave threshold resonance. Because the line shapes for such a resonance are not integrable functions of the energy, the resonance parameters depend on the prescriptions used to define them. In recent experimental analyses of the $D^0{\overline{D}}^0{\pi }^0$ channel, an event near the $D^{*0}{\overline{D}}^0$ threshold was assumed to come from $D^{*0}{\overline{D}}^0$ or $D^0{\overline{D}}^{*0}$ and was therefore assigned an energy above the threshold. Taking this effect into account, our analysis of the $D^0{\overline{D}}^0{\pi }^0$ data gives a mass for the $X(3872)$ that is below the $D^{*0}{\overline{D}}^0$ threshold. Our analyses in both the $J/\psi {\pi }^{+}{\pi }^{-}$ and $D^0{\overline{D}}^0{\pi }^0$ channels are consistent with the identification of the $X(3872)$ as an extremely weakly bound charm meson molecule.

• Received 14 December 2009

DOI:https://doi.org/10.1103/PhysRevD.81.014019