How can we unravel the mysteries of the XYZ states?

Abstract
In recent years many states were discovered both in the charmonium as well as in the bottomonium sector that do not fit into the standard quark model picture – this is especially true for the charged states Zb(10610), Zb(10650), Z(4430), Zc(3900) and Zc(4020)$. The nature of these states is heavily discussed in the literature. The most prominent proposals put forward are compact tetraquarks -- bound states of heavy diaquarks and heavy anti-diquarks --- hadroquarkonia --- a compact quarkonium core surrounded by a light quark cloud --- or hadronic molecules --- bound states of two color neutral mesons. In this talk I will discuss what is needed from the experimental side to distinguish amongst the different scenarios.

References

• Heavy quarkonium review of the particle data group
• N. Brambilla et al., ``Heavy quarkonium: progress, puzzles, and opportunities,'' Eur. Phys. J. C 71 (2011) 1534 [arXiv:1010.5827 [hep-ph]]