Investigation of the eta-prime meson structure and of the isospin dependence of its production in the nucleon-nucleon collisions


It is proposed to investigate the structure of the eta' meson and the mechanism of its creation in the nucleon-nucleon interaction by comparing its close to threshold production cross section in the proton-proton and proton-neutron collisions. The comparison of the ratio Reta' = sigma(pn->pn eta') / sigma(pp->pp eta') with Reta = sigma(pn->pn eta) / sigma(pp->pp eta) will allow to infer about the gluonium content of the eta' meson and the relevance of quark-gluon degrees of freedom when considering the close to threshold production of this meson.

In the extreme case when the eta' meson is created only from glue being excited in the interaction region the ratio Reta should be close to unity after the correction for the final and initial state interaction between the interacting nucleons. Whereas a production mechanism dominated by the isovector meson exchange would yield a significantly larger ratio. In the latter case it is expected to be close to a value of 6.5 as already determined for the etameson production. Together with already established excitation functions for the reactions pp->pp eta', pp->pp eta and partially also for pn->pn eta, the determination of the energy dependence of the total cross section for the pn->pn eta' reaction would strengthen significantly constraints on the analysis aiming at the determination of contributions from mesonic, gluonic, nucleonic and resonance currents to the production process.

In the test measurement, using a beam of protons and a deuteron cluster target, we have proven the ability of the COSY-11 facility to study the quasi-free creation of mesons via the pn->pnX reaction. In this proposal we would like to ask for altogether 8 weeks of COSY beam-time with an allocation of 4 weeks in the coming period in order to determine the excitation function of the pn->pn eta' reaction, in the excess energy range between Q = 0 MeV and Q = 30 MeV.

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