On The pp->pp\eta (eta') Reactions Near Threshold
  The production rate for \eta' in pp ->pp \eta' at rest is calculated in a covariant one boson exchange model, previously applied to study pi^0 and \eta production in NN collisions. The transition amplitudes for the elementary 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 s and u channels with a nucleon in the intermediate states, and a delta meson pole in a t-channel. The couplings of the eta' to hadrons are a factor 0.437 weaker than the respective eta-hadron couplings, as suggested by a quark model and a singlet-octetmixing angle theta = -23 degree. The model reproduces near threshold cross sections for the quasielastic processes pi- p ->n eta (eta') and pp -> pp eta (eta') reactions. 
E.Gedalin, A.Moalem and L.Razdolskaja