Study of the $\eta$-nucleus interaction in the $pd{\to }^{3}He\eta$ reaction near threshold

Abstract

A detailed study of the effect of the $\eta$-nucleus final state interaction (FSI) in the $pd{\to }^3$He$\eta$ reaction close to threshold is presented. The FSI is incorporated through a T-matrix for ${\eta }^3$He elastic scattering, constructed using few body equations. This T-matrix accounts for off-shell and binding effects in $\eta$-nucleus scattering. The energy dependence of the data on the $pd{\to }^3$He$\eta$ reaction near threshold is reproduced only after including the FSI. The off-shell and binding effects in ${\eta }^3$He scattering are found to be important. Given the uncertainty in the knowledge of the elementary $\eta$-nucleon interaction, the sensitivity of the $pd{\to }^3$He$\eta$ cross section to different prescriptions of the elementary t-matrix, $t_{\eta N\to \eta N}$ is also discussed.

Comments: 16 pages, LaTex, including 6 figures