Universal Spacing for Heavy Quarkonium Dissociation
  When a heavy quark and the corresponding antiquark are separated by more than $1.4 - 1.5$ fm, it becomes energetically favorable for a light quark-antiquark pair to be produced, leading to fragmentation into a pair of flavored mesons. The relation of this critical quark separation to other dimensional constants of the strong interactions (such as the pion decay constant, the QCD scale, and the light-quark constituent mass) is discussed. 
Jonathan L. Rosner