60 40 43 v 1 2 5 A pr 1 99 6 Near threshold η production in proton - proton collisions

The total cross section for the near threshold η production in proton-proton collisions has been investigated with the assumption that the production mechanism is due to the emission of a meson x(π, η, σ) from one of the nucleons followed by a xN → ηN transition on the second one. The xN → ηN amplitudes are generated from the unitary multi-channel multi-resonance model which has recently been constructed in analyzing the πN scattering and πN → ηN reaction. The initial and final pp distortions are calculated from a coupled-channel πN N model which describes the N N scattering data up to about 2 GeV. With the x − N N vertex functions taken from the Bonn potential, the predicted total cross sections of threshold pp → ηpp reaction are in good agreement with the data. In contrast to previous works, we find that the η-exchange plays an important role. The effect of the two-pion exchange, simulated by σ-exchange, is found to be significant but not as dominant as the vector meson-exchange introduced in previous works. The η production in proton-proton collisions has attracted a lot of interest in the past decade. A theoretical understanding of this two-nucleon process near the production threshold is needed for exploring the N * (S 11 (1535)) dy