Hadronic decays and soft-pion theorems in the charmonium model

Using the charmonium model for psi and psi', we show that the partial widths for decays into any ''normal'' hadronic final state n (i.e., any state including no particles which contain charmed quarks) must approximately satisfy GAMMA(psi' → n)/GAMMA(psi → n) approx. = GAMMA(psi' → e+e-)/GAMMA(psi → e+e-). So far this relation has been tested for n = pp-bar, 2π+2π-π0, and K+K-π+π-. We also derive the soft-pion theorem GAMMA(psi → n)/GAMMA(psi → e+e-) approx. = sigma(e+e- → n)/sigma(e+e- → μ+μ-), for any normal state n including a soft pion but no baryons. A number of similar predictions for other configurations of the charmed-quark--charmed-antiquark system are considered, and a related theorem is obtained which helps explain the pion momentum distribution observed in the decay psi' → psiπ+π-