pp→ppη′ reaction at high energies

We discuss double-diffractive (double-elastic) production of the eta(')-meson in the pp -> p eta(')p reaction within the formalism of unintegrated gluon distribution functions (UGDF). We estimate also the contribution of gamma(*)gamma(*)->eta(') fusion. The distributions in the Feynman x(F) (or rapidity), transferred four-momenta squared between initial and final protons (t(1),t(2)) and azimuthal angle difference between outgoing protons (Phi) are calculated. The deviations from the sin(2)(Phi) dependence predicted by one-step vector-vector-pseudoscalar coupling are quantified and discussed. The results are compared with the results of the WA102 collaboration at CERN. Most of the models of UGDF from the literature give a too small cross section as compared to the WA102 data and predict angular distribution in relative azimuthal angle strongly asymmetric with respect to pi/2 in disagreement with the WA102 data. This points to a different mechanism at the WA102 energy. Predictions for RHIC, Tevatron and LHC are given. We find that the normalization, t(1,2) dependences as well as deviations from sin(2)(Phi) of double-diffractive double-elastic cross section are extremely sensitive to the choice of UGDF. Possible implications for UGDFs are discussed.