Branching Fractions of the $X(3872)$

Understand

The recoil momentum spectrum from the decay $B^+ \to K^+ +\mathrm{anything}$ has recently been measured by the BaBar collaboration.

• The spectrum has a peak with invariant mass near the mass of the $X(3872)$ meson.
• The preliminary measurement by the BaBar collaboration implies that its branching fraction into $J/\psi\, \pi^+\pi^-$ is about 4\%.
• We emphasize that this is the branching fraction for the entire resonance feature from $B^+$-to-$K^+$ transitions, which includes a $D^{*0} \bar D^0$ and $D^0 \bar D^{*0}$ threshold enhancement as well as a possible bound state below the threshold or a virtual state.