Masses of the ηc(nS) and ηb(nS) mesons

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/psi - eta(c)(1S) and psi(2S) - eta'(c\)(2S) splittings and appears to be small, r(ss) approximate to 0.06 fin. Nevertheless, even with such a small radius an essential suppression of the hyperfine splittings (similar to 50%) is observed in bottomonium. For the nS b (b) over bar 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 3S and 4S charmonium states the splittings 16(2) and 12(4) MeV are obtained. (c) 2007 Elsevier B.V. All rights reserved.