Direct, Resonant Production of States with Positive Charge Conjugation in Electron-Positron Annihilation

Recent theory results on direct production of resonances with positive charge conjugation in electron-positron annihilation are reviewed. The strong model dependence is emphasized, with predictions varying between 0.03 eV and 0.43 eV for the charmonium state with $J^{PC}=1^{++}$ and between 0.16 eV and 4.25 eV for the state with $J^{PC}=2^{++}$. For the state with $J^{PC}=0^{++}$ the cross section is of $\mathcal{O}$ $(m_e^2\mathrm{/}{M}_{\chi }^2)$ and thus negligeable for all practical purpose. The importance of the relative phase of the production amplitude is emphasized.