Radiative decays ofψandψ′involvingqq¯scalar-meson final states

A study is made of the contributions of $q\overline{q}$ scalar mesons to the processes ${\psi }^{\prime }$, $\psi \to \gamma +\mathrm{hadrons}$. In particular, the decay widths for the exclusive channels ${\psi }^{\prime }$, $\psi \to \epsilon \mathrm{}\left(800\right)\mathrm{}\gamma$, ${\epsilon }^{\prime }\mathrm{}\left(1400\right)\mathrm{}\gamma$ are calculated using an extended version of vector-meson dominance for the electromagnetic interactions of hadrons. The strong couplings of the scalar mesons to $\psi$ and ${\psi }^{\prime }$ are determined from a scalar-meson-nonet-dominance description for ${\psi }^{\prime }\to \psi \pi \pi$. In the case of the $\psi$ resonance we find that the processes $\psi \to \epsilon \gamma$ and $\psi \to {\epsilon }^{\prime }\gamma$ yield a combined radiative width which is substantial and is consistent with recent inclusive measurements at SLAC as well as with calculations based on first-order quantum chromodynamics (QCD). A similar analysis of ${\psi }^{\prime }$ suggests that the $\epsilon \gamma$ and ${\epsilon }^{\prime }\gamma$ modes make a very small contribution to the ${\psi }^{\prime }$ radiative width. The branching ratios $\frac{\Gamma ({\psi }^{\prime }, \psi \to {\epsilon }^{\prime }\gamma )}{\Gamma ({\psi }^{\prime }, \psi \to \epsilon \gamma )}$ obtained by vector-meson dominance are found to be consistent with those predicted by leading-order QCD if one assumes that the emitted photon is a pure SU(3) singlet.