Breakup and coherent photoproduction of η meson on the deuteron

We have taken new breakup and coherent data for η meson photoproduction on the deuteron, using a deuterium target and tagged Bremsstrahlung photons up to 1 GeV (ELSA, Bonn). The differential cross sections from the coherent processes were measured between threshold and 800 MeV. They are much smaller than those previously reported, with an angular distribution in qualitative agreement with existing impulse approximation theoretical predictions. The breakup channels provide a direct measurement of the neutron to proton differential cross section ratios, with not much energy but significant angular dependence. At the S11 (1535) resonance peak, σn/σp = 0.68 ± 0.06 leading to an isoscalar to isovector amplitude ratio As/Av = 0.096 ± 0.02. (authors)