Coherent Neutral Pion and eta Meson Photoproduction on the Deuteron

Coherent photoproduction of the neutral pion and eta meson on the deuteron, γ d → π 0 η d , has been experimentally studied at E γ < 1.15 GeV. The total cross section as a function of the incident energy shows a rapid increasing behavior below 1 GeV. The existing theoretical calculations well-reproduce the data including final-state interactions. We have measured the differential cross sections d σ / d M π d , d σ / d M η d , and d σ / d Ω d in the γ d center-of-mass frame for the first time. An enhancement is observed near the η d threshold in d σ / d M η d , suggesting a strong η d attraction. The enhancement is consistent with a predicted isoscalar 1 - η N N bound state from the η N N and π N N coupled-channel calculation.