Coherent Neutral Pion and eta Meson Photoproduction on the Deuteron

Coherent photoproduction of the neutral pion and eta meson on the deuteron, gamma d ->lambda(0) eta d, has been experimentally studied at E-gamma < 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 havemeasured the differential cross sections d sigma/dM(pi d), d sigma/dM(eta d), and d sigma/d Omega(d) in the gamma d center-of-mass frame for the first time. An enhancement is observed near the.d threshold in d(s)/dM(eta d), suggesting a strong eta d attraction. The enhancement is consistent with a predicted isoscalar 1(-) eta NN bound state from the eta NN and pi NN coupled-channel calculation.