The ${Y_1}^{*+}-{Y_1}^{*-}$ mass difference is calculated, taking account of the contributions from (1) scalar-meson tadpoles, (2) intermediate states involving one ${Y_1}^{*}$ and one photon, and (3) intermediate states involving one $\Sigma$ and one photon. The sum of these yields a mass splitting of between -8.5 and -10.8 MeV. The experimental value is -17±7 MeV.

• Received 13 May 1964

DOI:https://doi.org/10.1103/PhysRev.135.B1451