Study of meson production in nuclei near threshold

We present a study of the η production at low energies in pd collision with ³He and pd nuclear systems in the final state. The η production mechanism is described by a two-step model and the final state interactions are included fully. The η - d and η - ³He final state interactions are incorporated through the solution of the Lippmann Schwinger equation for a half off-shell η - AT-matrix. For η - d this t-matrix is written in a factorized form, with an off-shell form factor multiplying an on-shell part having the scattering length representation. The p - d final state interaction is included by multiplying the production matrix element by the inverse of the Jost function which includes the strong as well as the Coulomb interaction. The total cross sections are found to be strongly affected by both the η - d and the p - d final state interactions. The η - ³HeT-matrix is obtained in the Finite Rank Approximation (FRA) by solving few-body equations. The calculated total cross sections are in good accord with the available experimental data. Through the time delay method of Wigner, we also explore the possibility of the existence of quasi-bound η-³He mesic states in this η - ³HeT-matrix. We find that the T-matrix which reproduces the low energy pd → ³He η data implies a quasi-bound eta state near threshold. This is in accord with experimental indications. (author)