Electroexcitation of nucleon resonances at Q^2=0.65 GeV/c^2 from a   combined analysis of single- and double-pion electroproduction data
  Data on single- and double-charged pion electroproduction off protons are successfully described in the second and third nucleon resonance regions with common N* photocouplings. The analysis was carried out using separate isobar models for both reactions. From the combined analysis of two exclusive channels, the gamma* p --> N*+ helicity amplitudes are obtained for the resonances P11(1440), D13(1520), S31(1620), S11(1650), F15(1680), D33(1700), D13(1700), and P13(1720) at Q2=0.65 GeV/c^2. 
I.G. Aznauryan, V.D.Burkert, G.V. Fedotov, B.S. Ishkhanov, V.I. Mokeev