Bound-state spectroscopy of superheavy quarks

The transition to the exact positronium spectrum is studied as a function of quark mass. It is shown that, in the nonrelativistic potential approach, only for quarks as heavy as 100 GeV might one expect to see the level structure originally attributed to charmonium. It is also noted that in the hypothetical case that superheavy quarks exist one may directly produce via the weak current their 1++ bound states in future e+e- experiments. © 1977 The American Physical Society.