Near threshold η production in proton-proton collisions

The total cross sections 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 nucleon. The xN → ηN amplitudes are generated from the unitary multi-channel multi-resonance model which has recently been constructed by fitting the data of πN elastic scattering and πN → ηN reaction. The initial and final pp distortions are calculated from a coupled-channel πNN model which describes the NN scattering data up to about 2 GeV. With the xNN 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.