Study of the $η$-nucleus interaction in the $p d \to ^3He η$ reaction near threshold

Abstract

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