Energy dependence of the analysing power Ay(Thetaq*) for the p(pol)p->pp eta reaction


It is proposed to study the production mechanism of the eta meson in near threshold proton-proton collisions via the measurement of the energy dependence of the analysing power Ay(Thetaq*) for the p(pol)p->pp eta reaction in the excess energy range between threshold and 40 MeV.

The determination of that dependence would allow to establish the exchange processes which lead to the excitation of the S11 nucleon isobar in the proton-proton reaction, whose subsequent decay results in the creation of the eta meson. Theangular dependence of Ay in the excess energy range of the s-wave dominance will also permit to derive a magnitude of the small admixtures of the higher partial waves via the determination of the interference terms, which are inaccessible from the distributions of the spin averaged observables. The more precisely these contributions are known the more accurate are inferences concerning the production dynamics of the eta meson and the eta-proton interaction.

Guided by the predictions based on the dominance of the rho meson exchange model - favoured slightly by our previous measurement performed at the excess energy of Q = 40 MeV - we would like to measure the angular dependence of the eta meson analysing power Ay(Thetaq*) at Q = 2 MeV, 10 MeV, and 25 MeV, complementary to the investigations carried out at higher energies by the TOF collaboration. The realisation of the proposed investigation requires 7 weeks of beam time in total, which we would like to divide into two runs with 3 weeks in the coming period.

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