Exes and why Z? Some charming and beautiful observations

Understand

Threshold enhancements like the X(4660) and depletion effects as the X(4260) are listed as c-cbar resonances in the Particle Data Group tables.

• We will discuss these observations, and present a list of further c-cbar enhancements, which are more likely to represent true vector charmonium excitations.
• We will furthermore discuss the importance of the observed Z resonances, viz.
• Z(4050), Z(4250), and Z(4430), for the family of charm-strange mesons.