New results from the studies of the N(1440)1/2+, N(1520)3/2-, and Δ(1620)1/2- resonances in exclusive ep → e′p′π+π- electroproduction with the CLAS detector

The transition helicity amplitudes from the proton ground state to the N(1440)1/2(+), N(1520)3/2(-), and Delta(1620)1/2(-) resonances (gamma(v)pN* electrocouplings) were determined from the analysis of nine independent onefold differential pi(+)pi(-)p electroproduction cross sections off a proton target, taken with CLAS at photon virtualities 0.5 GeV2 < Q(2) < 1.5 GeV2. The phenomenological reaction model employed for separation of the resonant and nonresonant contributions to this exclusive channel was further developed. The N(1440)1/2(+), N(1520)3/2(-), and Delta(1620)1/2(-) electrocouplings were obtained from the resonant amplitudes of charged double-pion electroproduction off the proton in the aforementioned area of photon virtualities for the first time. Consistent results on gamma(v)pN* electrocouplings available from independent analyses of several W intervals with different nonresonant contributions offer clear evidence for the reliable extraction of these fundamental quantities. These studies also improved the knowledge on hadronic branching ratios for the N(1440)1/2(+), N(1520)3/2(-), and Delta(1620)1/2(-) decays to the pi Delta and rho N final states. These new results provide a substantial impact on the QCD-based approaches that describe the N* structure and demonstrate the capability to explore fundamental ingredients of the nonperturbative strong interaction that are behind the excited nucleon state formation.