Z_c(3900) - what is inside?

TL;DR

This paper reviews various models of the internal structure of the Z_c(3900) resonance, discussing how measurements of quantum numbers and decay channels can distinguish between molecular, hadro-charmonium, and tetraquark models.

Contribution

It proposes a method to differentiate models of Z_c(3900) by combining quantum number measurements and decay rate analysis of specific channels.

Findings

Different models predict distinct decay channels and quantum numbers.

Measurement of decay rates into specific channels can identify the correct model.

Related four-quark states are predicted and can be searched for in data.

Abstract

The models for the internal structure of the newly found four-quark charmonium-like resonance $Z_c(3900)$ are discussed: the molecular model as well as the hadro-charmonium and tetraquark schemes. It is argued that it would be possible to resolve between these models by combining measurements of the quantum numbers of the resonance and of its decay rates into yet unseen channels $\pi \psi'$, $\pi h_c$, $\rho \eta_c$ and into pairs of heavy mesons $D^* \bar D$ and $D \bar D^*$. The models also predict different related four-quark states, which can be sought for in the existing and future data.