Coherent $η$-photoproduction on $^4$He and $^{12}$C in the near-threshold region

Abstract

Coherent $η$ meson photoproduction on $^4$He and $^{12}$C is considered in the near-threshold region. The elementary $η$ photoproduction operator includes contributions from the $S_{11}(1535)$ and $D_{13}(1520)$ resonances as well as $t$-channel vector meson exchange and the nucleon pole terms. Due to the suppression of the dominant $S_{11}(1535)$ resonance for spin and isospin saturated nuclei, the reaction is mainly governed by $ω$ exchange. Furthermore, the influence of Fermi motion and of different prescriptions for the choice of the invariant reaction energy $W_{γN}$ in the elementary amplitude is studied.

27 pages revtex including 9 postscript figures