Amplitude analysis and the nature of the Zc(3900)
  The microscopic nature of the XYZ states remains an unsettled topic. We show how a thorough amplitude analysis of the data can help constraining models of these states. Specifically, we consider the case of the Zc(3900) peak and discuss possible scenarios of a QCD state, virtual state, or a kinematical enhancement. We conclude that current data are not precise enough to distinguish between these hypotheses, however, the method we propose, when applied to the forthcoming high-statistics measurements should shed light on the nature of these exotic enhancements. 
JPAC Collaboration: A. Pilloni, C. Fernandez-Ramirez, A. Jackura, V.   Mathieu, M. Mikhasenko, J. Nys, A.P. Szczepaniak
hep-ph nucl-th