How to extract the P33(1232) resonance contributions from the amplitudes M1+3/2,E1+3/2,S1+3/2 of pion electroproduction on nucleons

Within the dispersion relation approach, solutions of integral equations for the multipoles M1+3/2,E1+3/2,S1+3/2 are found at 0 < Q2 < 3 GeV2. These solutions should be used as input for the resonance and nonresonance contributions in the analyses of pion electroproduction data in the P33(1232) resonance region. It is shown that the traditional identification of the amplitude M1+3/2 (as well of the amplitudes E1+3/2,S1+3/2) with the P33(1232) resonance contribution is not right; there is a contribution in these amplitudes which has a nonresonance nature and is produced by rescattering effects in the diagrams corresponding to the nucleon and pion poles. This contribution is reproduced by the dispersion relations. Taking into account nonresonance contributions in the amplitudes M1+3/2,E1+3/2, the helicity amplitudes Ap1/2, Ap3/2 and the ratio E2/M1 for the γN rarrow P33(1232) transition are extracted from experiment at Q2=0. They are in good agreement with quark model predictions