The Isospin Splittings of Heavy-Light Quark Systems

The isospin mass splittings of the pseudoscalar and vector D and B light-heavy quark system have been calculated using the method of QCD sum rules. Nonperturbative QCD effects are shown to be very small, so that mass splittings arise almost completely from current quark mass splitting and electromagnetic effects, for which a new gauge invariant QED treatment is used. The results are consistent with experiment. A measurement of the isospin splitting of the vector B mesons would give valuable information about quark mass splittings.