pp→ppη′ reaction at high energies

We discuss double-diffractive (double-elastic) production of the η′-meson in the pp→pη′p reaction within the formalism of unintegrated gluon distribution functions (UGDF). We estimate also the contribution of γ*γ*→η′ fusion. The distributions in the Feynman xF (or rapidity), transferred four-momenta squared between initial and final protons (t1,t2) and azimuthal angle difference between outgoing protons (Φ) are calculated. The deviations from the sin 2(Φ) 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 π/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, t1,2 dependences as well as deviations from sin 2(Φ) of double-diffractive double-elastic cross section are extremely sensitive to the choice of UGDF. Possible implications for UGDFs are discussed. © 2007 The American Physical Society.