NEAR-THRESHOLD ETA-PRODUCTION IN PROTON-PROTON COLLISIONS

The total cross sections for the near threshold eta production in prot on-proton collisions has been investigated with the assumption that th e production mechanism is due to the emission of a meson chi(pi eta si gma from one of the nucleons followed by a chi N --> eta N transition on the second nucleon. The chi N --> eta N amplitudes are generated fr om the unitary multi-channel multiresonance model which has recently b een constructed by fitting the data of pi N elastic scattering and pi N --> eta N reaction. The initial and final pp distortions are calcula ted from a coupled-channel pi NN model which describes the NN scatteri ng data up to about 2 GeV. With the chi NN vertex functions taken from the Bonn potential, the predicted total cross sections of threshold p p --> eta pp reaction are in good agreement with the data. In contrast to previous works, we find that the eta-exchange plays an important r ole.