Isobar channels and nucleon resonances in π+π− electroproduction on protons

Acomprehensive set of differential cross sections for the reaction γνp → π−π+p at the square of the photon 4-momentum in the range 0.2 < Q2 < 0.6 GeV2 and the invariant mass of final-state hadrons in the range 1.3 < W < 1.6 GeV was first obtained with the CLAS detector at the Thomas Jefferson Laboratory. An analysis of these data on the basis of the phenomenological model developed by physicists from the Institute of Nuclear Physics at Moscow State University (INP MSU) and Thomas Jefferson Laboratory (INP MSU-Hall B at Jefferson Lab Collaboration) made it possible to determine, for the first time, the contributions of all isobar channels to the differential cross sections in question. The possibility of extracting the Q2 dependences of the electromagnetic form factors for the P11(1440) and D13(1520) resonances in a kinematical region that is the most sensitive to the contribution of the meson-baryon cloud to the structure of nucleon resonances is demonstrated.