A kinematical basis for power form factors

Abstract

A kinematical basis is proposed for form factors of the power type associated with multiple derivative couplings, on the basis of a Lorentz contraction effect on the external momenta involved in the transition matrix elements for mesons and baryons as appropriate quark composites. The argument (due to Licht and Pagnamenta) which applies separately to the Breit and c.m. frames for a decay matrix element provides a formal theoretical justification for thead hoc power form factors used by the Delhi group in a series of applications to hadronic processes over the past few years. The radius of interaction finds a natural place in this description simply from dimensional considerations, and its rather small magnitude, less than 0.5F, estimated fromfits to the data indicates a relatively small role played by structure effects. The Breit frame form factors, which work somewhat better than the c.m. frame ones (effectively used in the earlier studies), give a rather impressive sets of fits to the baryon decays in the (L + 1) wave (consistently for both vertical and horizontal) and the (L − 1) wave (mainly horizontal). The mesonic decays, the data for which are available mostly for the (L + 1) wave, are also fitted with an equal degree of consistency without any extra assumptions.