A meson-exchange model of the associated photoproduction of vector mesons and N * (1440) resonances

We discuss the photoproduction of omega- and rho(0)-mesons off protons in t he particular channel where the target proton is excited to a Roper resonan ce N*(1440). We propose a simple meson-exchange model for these processes i n order to evaluate their cross sections near threshold and at low momentum transfers. It is suggested in particular that the differential cross secti on for the associated photoproduction of a rho(0)-meson and a Roper resonan ce in these kinematic conditions could provide direct information on the st rength of the scalar-isoscalar excitation of the N*(1440) and hence on the magnitude of an effective sigma NN *(1440) coupling. The latter quantity is poorly known and of much interest for the nuclear many-body problem. (C) 2 000 Elsevier Science B.V. All rights reserved.