Understanding the nature of the heavy pentaquarks and searching for them   in pion-induced reactions
  We investigate the reaction $\pi^- p \to \pi^- J/\psi p$ via the open-charm hadron rescattering diagrams. Due to the presence of the triangle singularity (TS) in the rescattering amplitudes, the TS peaks can simulate the pentaquark-like resonances arising in the $J/\psi p$ invariant mass distributions, which may bring ambiguities on our understanding of the nature of the exotic states. Searching for the heavy pentaquark in different processes may help us to clarify the ambiguities, because of the highly process-dependent characteristic of the TS mechanism. 
Xiao-Hai Liu and Makoto Oka
hep-ph hep-ex nucl-ex nucl-th