The transition helicity amplitudes from the proton ground state to the P11(1440) and D13(1520) excited states (γvpN∗ 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
Physical Review C
Mokeev, V.; Biselli, Angela; and CLAS Collaboration, "Experimental study of the P11(1440) and
D13(1520) resonances from the CLAS data on ep→e′π+π−p" (2012). Physics Faculty Publications. 20.
V. Mokeev et al. [CLAS Collaboration], "Experimental study of the P11(1440) and D13(1520) resonances from the CLAS data on ep→e′π+π−p′" Physical Review C, Volume 86, Issue 3, 035203 (2012). DOI: 10.1103/PhysRevC.86.035203