NEAR-THRESHOLD PHOTOPRODUCTION OF ETA-MESONS FROM THE DEUTERON

The first measurement of incoherent eta-photoproduction from the deute ron in the threshold region is reported. The experiment was carried ou t at the MAMI accelerator with the TAPS spectrometer. Total and differ ential inclusive cross sections have been obtained between 627 and 790 MeV. it is found that the reaction is completely dominated by the inc oherent part. An upper limit for coherent eta-photoproduction on the d euteron is deduced, which is substantially lower than the result from an earlier measurement. The incoherent cross section is reproduced in a participant-spectator approach under the assumption of an energy-ind ependent ratio between the neutron and proton cross sections. Best agr eement is found for the ratio sigma(n)/sigma(p) approximate to 2/3. Th e implications for the isospin components of the electromagnetic excit ation of the S-11(1535) resonance are discussed.