Amplitude analysis and the nature of the Zc(3900)

Understand

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.