The transition helicity amplitudes from the proton ground state to the P11(1440) and D13(1520) excited states (vγpN* electrocouplings) were determined from the analysis of nine independent one-fold differential π+π−p electroproduction cross sections off a proton target, taken with CLAS at photon virtualities of 0.25 < Q2 < 0.60 GeV2. The phenomenological reaction model was employed for separation of the resonant and nonresonant contributions to the final state. The P11(1440) and D13(1520) electrocouplings were obtained from the resonant amplitudes parametrized within the framework of a unitarized Breit-Wigner ansatz. They are consistent with results obtained in the previous CLAS analyses of the π+n and π0p channels. The successful description of a large body of data in dominant meson-electroproduction channels off protons with the same γvpN* electrocouplings offers clear evidence for the reliable extraction of these fundamental quantities from meson-electroproduction data. This analysis also led to the determination of the long-awaited hadronic branching ratios for the D13(1520) decay into Δπ(24%–32%) and Nρ (8%–17%).
Copyright © 2012 American Physical Society. This article first appeared in Physical Review C 86, no. 3 (September 13, 2012): 035203:1-22. doi:10.1103/PhysRevC.86.035203.
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