An Isobar Model for η - and Electroproduction on the Nucleon

An isobar model containing Born terms, vector meson exchange and nucleon resonances is used to analyze recent η photoproduction data for cross sections and beam asymmetries, as well as JLab electroproduction data. Good overall description is achieved up to Q² = 4.0 (GeV/c)². Besides the dominant S₁₁(1535) resonance, we show that the second S₁₁ resonance, S₁₁(1650), is also necessary to be included in order to extract the S₁₁(1535) resonance parameters properly. In addition, the beam asymmetry data allow us to extract very small (< 0.1%) N* → ηN decay branching ratios of the D₁₃(1520) and F₁₅(1680) resonances because of the overwhelming s-wave dominance. The model is implemented as a part of the MAID program.