Threshold region photoproduction of neutralπmesons off complex nuclei

Abstract

Photoproduction of ${\ensuremath{\pi}}^{0}$ mesons off targets of $^{6}\mathrm{Li}$, $^{12}\mathrm{C}$, $^{28}\mathrm{Si}$, $^{40}\mathrm{Ca}$, natural Cd, and natural Pb was studied using a bremsstrahlung beam with endpoint energies of 140, 145, 150, and 155 MeV. Photoproduction from a liquid hydrogen target was employed as a normalization. The measured yields were found to be in disagreement with published theoretical cross sections for $^{6}\mathrm{Li}(\ensuremath{\gamma}, {\ensuremath{\pi}}^{0})^{6}\mathrm{Li}$ and also in disagreement with a simple schematic model which assumed only coherent contributions from the ${M}_{1+}$ multipole. The schematic model, however, did approximately predict the relative magnitudes of the yield curves for the energy range 14-20 MeV over threshold.NUCLEAR REACTIONS $^{6}\mathrm{Li}$, $^{12}\mathrm{C}$, $^{28}\mathrm{Si}$, $^{40}\mathrm{Ca}$, Cd, Pb, ($\ensuremath{\gamma}, {\ensuremath{\pi}}^{0}$); ${E}_{\ensuremath{\gamma}}=140\ensuremath{-}155$ MeV; measured $\ensuremath{\sigma}$; test of reaction model.