Masses of the ? c ( n S ) and ? b ( n S ) mesons

Abstract The hyperfine splittings in heavy quarkonia are studied using new experimental data on the di-electron widths. The smearing of the spin–spin interaction is taken into account, while the radius of smearing is fixed by the known J / ψ − η c ( 1 S ) and ψ ( 2 S ) − η c ′ ( 2 S ) splittings and appears to be small, r s s ≈ 0.06 fm. Nevertheless, even with such a small radius an essential suppression of the hyperfine splittings ( ∼ 50 % ) is observed in bottomonium. For the nS b b ¯ states ( n = 1 , 2 , … , 6 ) the values we predict (in MeV) are 28, 12, 10, 6, 6, and 3, respectively. In single-channel approximation for the 3 S and 4 S charmonium states the splittings 16(2) and 12(4) MeV are obtained.