CHARMONIUM AND UPSILON-SYSTEMS WITH SMALL HYPERFINE SPLITTINGS

The parameters of the simple Coulomb plus linear effective potential with lowest-order relativistic corrections are determined by the charmonium states other than the S01 states and by the leptonic decay widths of Jψ and ψ′. The effective coupling constant αs is found to be 0.21. Within this framework the hyperfine splittings are small and so are the consequent M 1 transitions (well below the experimental upper limit of 1.2 keV). The S01 partners of ψ and ψ′ are predicted to be ηc(3020) and ηc′(3638) and are not to be identified with the experimentally uncertain X(2830) and χ(3450). The same effective potential, chainging only the constituent quark mass, gives a good description of the system. The spin-independent relativistic corrections play an important role in obtaining the equality m′-mmψ′-mψ. © 1979 The American Physical Society.