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

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^P C = 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^P C quantum numbers. Most notably, we find that all states with C · P = +1 are dominated by heavy-light meson contributions, whereas for axialvector states with J^P C = 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.