Eta Photoproduction on the Proton

Eta photoproduction experiments have proven a useful tool in the search for narrow nucleon resonances. In recent years, there has been much interest in the possible existence of the N*(1685) narrow nucleon resonance. Several experiments have been performed that rely on extracting neutron observables from deuteron target data. These have shown some evidence of narrow structure, however, no structure was observed on the proton channel. Within the A2 collaboration at Mainz, a more detailed study has been undertaken using eta photoproduction on an LH2 target (γp → ηp); it has high resolution and high precision, in an attempt to overcome the predicted low photocoupling between the N*(1685) and the proton. This paper provides an overview of the experiment and detector systems, and shows the current state of the data analysis. The γp → ηp total cross section is presented for the 2γ η-decay channel. This shows no evidence of the N*(1685) in η photoproduction on the proton.