Study of the gluon content of the eta-prime meson via its close-to-threshold production in the nucleon-nucleon collisions


The most remarkable feature - in the frame of the quark model - distinguishing the eta' meson from all other pseudscalar and vector ground state mesons, is the fact, that the eta' is predominantly a flavour-singlet combination of quark-antiquark pairs and therefore can mix with purely gluonic states.

Therefore, additionally to the mechanisms associated with meson exchanges it is possible that the eta' meson is created from excited glue in the interaction region of the colliding nucleons, which couple to the eta' meson directly via its gluonic component or through its SU(3)-flavour-singlet admixture. The production through the colour-singlet object as suggested in reference [1] is isospin independent and should lead to the same production yield of the eta' meson in the pn -> pn gluons -> pn eta' and pp -> pp gluons -> pp eta' reactions after correcting for the final and initial state interaction between the nucleons.

In this presentation we will argue that a comparison of the close-to-threshold total cross sections for the eta' meson production in both the pp -> pp eta' and pn -> pn eta' reactions should provide insight into the flavour-singlet (perhaps also into gluonium) content of the eta' meson and the relevance of quark-gluon or hadronic degrees of freedom in the creation process [2]. We will present experimental technique used for the measurements of the eta and eta' meson production in free proton-proton and quasi-free proton-neutron collisions. Tentative results from the measurements carried out at the COSY-11 facility using a beam of stochastically cooled protons and the deuteron cluster target will be presented and discussed.

S.D.Bass, Phys. Lett. B 463 (1999) 286, [e-Print Archive: hep-ph/9907373]
P.Moskal, e-Print Archive: hep-ph/0408162

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