S-wave production cross section of the pd → 3Heη reaction near threshold

The pd → 3Heη reaction at energies near threshold is studied in a nonrelativistic boson exchange model, where the P33 Δ (1232 MeV) and the 511 N* (1535 MeV) resonances are excited through the exchange of rg q and p mesons. This is an ex- tension of a previous model for η production in NN collisions which brings new insights into the production mechanisms of heavy mesons in hadronic interactions between nuclei. The momentum transfer involved is high due to the large mass of the q and therefore the contributions of a single step mechanism, where there is a spectator nucleon, are highly suppressed. The dominant contribution to the amplitude involves double scattering graph where there are no spectator particles, allowing the momentum transfer to be shared between all nucleons in the 3He nucleus. Under these conditions, the P33 ii (1232 MeV) resonance which plays no role at all in the two nucleon sector, can now be excited in the first step of the process. The total cross section is found to be dominated by three-nucleon mechanisms in which the q is produced via consecutive excitations of a ii (1232 MeV) P33 and a N* (1535 MeV) S11 resonances. The contributions from three nucleon mechanisms involving the excitation of two 511 N* (1535 MeV) resonances or two nucleon mechanisms, are found to be rather small. Providing the strong final-state interaction of the q with the 3He nucleus is taken into account, the predicted energy dependence of the cross section agrees well with recent measurements though the scale of the calculated cross section differs by a factor of ∼ 2. The analyzing power is found to be ∼ 0.60. (authors)