Hidden-flavour four-quark states in the charm and bottom region

Abstract

We discuss the spectrum and the internal composition of ground and excited four-quark states in the charm and bottom energy region. To this end we extend previous calculations within the framework of the relativistic four-body Faddeev-Yakubovsky equation to include quantum numbers with $J^{PC}=0^{++},0^{-+},1^{--},1^{+-}$ and $1^{++}$ and study their internal composition in terms of heavy-light meson pairs, hadroquarkonia and diquark-antidiquark clusters. We observe similar patterns in the charm and bottom energy region with different compositions of the four-quark states depending on $J^{PC}$ quantum numbers. Most notably, we find that all states with $C\cdot P=+1$ are dominated by heavy-light meson contributions, whereas for axialvector states with $J^{PC}=1^{+-}$ including the $Z_c(3900)$ we find a much more complicated picture depending on the flavour content. We systematically compare our results for the spectrum with existing experimental results and provide predictions for future analyses.

Comments: 14 pages, 11 figures