Electromagnetic Structure of the Z_c(3900)

TL;DR

This paper investigates the electromagnetic properties of the Z_c(3900) exotic state, interpreting it as a hadronic molecule and calculating its form factors and radii using effective theory, supported by experimental data.

Contribution

It provides the first detailed theoretical analysis of Z_c(3900)'s electromagnetic structure as a hadronic molecule, including form factors and radii calculations at next-to-leading order.

Findings

Calculated form factors and charge/magnetic radii for Z_c(3900)

Interpreted Z_c(3900) as an S-wave hadronic molecule

Provided numerical estimates at leading order

Abstract

The observation of the exotic quarkonium state Z_c(3900) by the BESIII and Belle collaborations supports the concept of hadronic molecules. Charmonium states interpreted as such molecules would be bound states of heavy particles with small binding energies. This motivates their description using an effective theory with contact interactions. In particular, we focus on the electromagnetic structure of the charged state Z_c(3900). Using first experimental results concerning spin and parity, we interpret it as an S-wave molecule and calculate the form factors as well as charge and magnetic radii up to next-to-leading order. We also present first numerical estimations of some of these observables at leading order.