A COVARIANT OBE MODEL FOR ETA-PRODUCTION IN NN COLLISIONS

A relativistic covariant one boson exchange model, previously applied to describe elastic nucleon-nucleon scattering, is extended to study e ta production in NN collisions. The transition amplitudes for the elem entary BN --> eta N processes with B being the meson exchanged (B = pi , sigma, eta, rho, omega and delta) are taken to be the sum of four te rms corresponding to s and u-channels with a nucleon or a nucleon isob ar N (1535 MeV) in the intermediate states. Taking the relative phase s of the various exchange amplitudes to be +1, the model reproduces th e cross sections for the NN --> X eta reactions in a consistent manner . In the limit where all eta's are produced via N excitations, interf erence terms between the overall contribution from the exchange of pse udoscalar and scalar mesons with that of vector mesons cancel out. Con sequently, much of the ambiguities in the model predictions due to unk nown relative phases of different vector and pseudoscalar exchanges ar e strongly reduced. (C) 1998 Published by Elsevier Science B.V.