ISOBAR CHANNELS IN THE PRODUCTION OF PI+ PI- PAIRS ON A PROTON BY VIRTUAL PHOTONS

A new approach is developed for evaluating contributions of various isobar channels to the double charged-pion production in the reactions γr,vp → π+π−p. This approach makes it possible to determine both respective cross sections and amplitudes for quasi-two-particle channels from a fit to data on cross sections for a three-particle final state. The diffractive anzatz, which is widely used to describe rho-meson production, is modified to meet the purpose of the description of data in the near-threshold and subthreshold regions. The cross sections for rho-meson electroproduction in the energy region of nucleon-resonance excitation are determined for the first time on the basis of the latest data of the CLAS Collaboration.