Contribution Leading parallel
Triangle singularities in production of X(3872)
If the X(3872) is a weakly bound charm-meson molecule, it can be produced by the creation of $D^ \bar D^$ at short distances followed by the rescattering of the charm mesons into X(3872) and a photon or a pion through a triangle loop. A triangle singularity produces narrow peak in the reaction rate in production of X(3872). The observation of this peak would provide strong evidence in support of the identification of the X(3872) as a charm-meson molecule.