$B_c$ spectroscopy

In the framework of potential models for heavy quarkonium the mass spectrum for the system (¯ bc ) is considered. Spin-dependent splittings, taking into account a change of a constant for effective Coulomb interaction between the quarks, and widths of radiative transitions between the (¯ bc ) levels are calculated. In the framework of QCD sum rules, masses of the lightest vector B ∗ c and pseudoscalar B c states are estimated, scaling relation for leptonic constants of heavy quarkonia is derived, and the leptonic constant f B C is evaluated.