Off-mass-shell coupling constants and radiative decays of ψ particles in VDM

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Abstract
A class of radiative decays of psi particles is studied in the vector-meson dominance model to determine the behaviour of the off-shell vector-meson-photon coupling constants. It is found that these are suppressed by about a couple of orders of magnitude compared with their on-shell values and the suppression thus obtained may be much larger than is usually believed. Different approaches for the incorporation of the suppression in simple VDM are discussed, and the necessity of considering suppression due to off-shell effects at both the hadronic and photonic vertices is emphasised. While the authors' model is constructed in the constructive interference scheme, the parallel arguments in the cancellation hypothesis are closely examined in an appendix to the paper; it is found that in this hypothesis also off-shell suppression factors are necessary to give currently acceptable numbers, and some of the problems associated with this approach are indicated.