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Description
We discuss central exclusive production (CEP) of $\eta$ and $\eta'(958)$ mesons in diffractive proton-proton collisions at high energies [1]. The amplitudes, including pomeron and $f_{2 R}$-reggeon exchanges, are calculated within the tensor-pomeron model. Absorption effects are also taken into account at the amplitude level. We fit some undetermined model parameters (coupling constants and cutoff parameters in form factors) to the WA102 experimental data and then make predictions for the LHC energy $\sqrt{s} = 13$ TeV. Cross sections and differential distributions are presented and discussed. For $pp \to pp \eta$, we find an upper limit for the total cross section of 2.5 $\mu$b for pseudorapidity of the $\eta$ meson $|\eta_{M}| < 1$ and 5.6 $\mu$b for $2 < \eta_{M} < 5$. For $pp \to pp \eta'$, we predict the cross section to be in the range of 0.3--0.7 $\mu$b for pseudorapidity of the $\eta'$ meson $|\eta_{M}| < 1$ and 0.9--2.1 $\mu$b for $2 < \eta_{M} < 5$. This opens the possibility to study diffractive production of pseudoscalar mesons in experiments at the LHC.
We also discuss CEP of the pseudovector meson $f_{1}(1285)$ in diffractive proton-proton collisions. We show that for a scalar pomeron these pomeron-pomeron fusion reactions are not possible. Thus, experimental observation of any of these particles in the above CEP processes at the LHC would give striking evidence against a scalar character of the pomeron.
[1] Central exclusive production of $\eta$ and $\eta'$ mesons in diffractive proton-proton collisions at the LHC within the tensor-pomeron approach, Phys. Rev. D112 (2025) 3, 034016
