Isobar Analysis ofγp→ηp

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Abstract
An analysis of the available data below 2.24-GeV c.m. energy for the process γp→ηp yields values of G≡Γ(R→γp)Γ(R→ηp) for several s-channel resonances, R. By varying the details of the direct-channel isobar model it is found that the values of G are reasonably model-independent. When these values are combined with information from other reactions it is possible to calculate electromagnetic widths for the important resonance states in this process. These include essential contributions from S11 and P11 states; in addition, admixtures of P13, D13, F17, and G17 resonances are also needed in order to obtain a good fit to the data. An excellent fit is found by including some recently conjectured stray baryonic states which do not couple significantly to the πN channel.