Differential cross sections for coherent and incoherent neutral-pion photoproduction from calcium

Differential and absolute cross sections for the coherent reaction $^{40}\mathrm{Ca}$(\ensuremath{\gamma},${\ensuremath{\pi}}^{0}$${)}^{40}$Ca g.s., as well as for the incoherent reaction $^{40}\mathrm{Ca}$(\ensuremath{\gamma},${\mathrm{\ensuremath{\pi}}}^{0}$${)}^{40}$Ca(g.s.), have been measured with monochromatic photons in the threshold region (${E}_{\ensuremath{\gamma}}$=157--169 MeV). The differential cross section for the coherent process exhibits a diffraction minimum due to the nuclear mass form factor while the incoherent cross section is rather structureless. The cross sections are in good agreement with recent distorted-wave impulse-approximation calculations.