Break-up and Coherent Photoproduction ofηMesons on the Deuteron

We present new break-up and coherent data for $\ensuremath{\eta}$ meson photoproduction on the deuteron, using a deuterium target and tagged bremsstrahlung photons up to 1 GeV. The differential cross sections for the coherent process were measured from threshold to 800 MeV. They are much smaller than those previously reported. The break-up channel provides a direct measurement of the neutron to proton differential cross section ratios. At the ${S}_{11}(1535)$ resonance peak, ${\ensuremath{\sigma}}_{n}/{\ensuremath{\sigma}}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.68\ifmmode\pm\else\textpm\fi{}0.06$ leading to an isoscalar to isovector amplitude ratio of ${A}_{s}{/A}_{\ensurem…