Central exclusive production as a probe of the gluonic component of the eta' and eta mesons

Currently, the long-standing issue concerning the size of the gluonic content of the eta' and eta mesons remains unsettled. With this in mind we consider the central exclusive production (CEP) of eta', eta meson pairs in the perturbative regime, applying the Durham pQCD-based model of CEP and the `hard exclusive' formalism to evaluate the meson production subprocess. We calculate for the first time the relevant parton-level processes gg --> qqbar gg and gg --> gggg, where the final-state gg and qqbar pairs form a pseudoscalar flavour-singlet state. We observe that these amplitudes display some non-trivial and interesting theoretical properties, and we comment on how this can be understood in a MHV framework. Finally, we present a phenomenological study, and show that the cross sections for the CEP of eta', eta meson pairs are strongly sensitive to the size of the gluon content of these mesons. The observation of these processes could therefore provide important and novel insight into this problem.