Document Type


Publication Date




Publication Title

Physical Review C






045209 (1-7)


The helicity amplitudes of the electroexcitation of the Roper resonance are extracted for 1.7 < Q2 < 4.5 GeV2 from recent high precision JLab-CLAS cross section and longitudinally polarized beam asymmetry data for π+ electroproduction on protons at W=1.15-1.69 GeV. The analysis is made using two approaches, dispersion relations and a unitary isobar model, which give consistent Q2 behavior of the helicity amplitudes for the gamma*p -> N (1440)P11 transition. It is found that the transverse helicity amplitude A 1/2, which is large and negative at Q2=0, becomes large and positive at Q2 similar or equal to 2 GeV2, and then drops slowly with Q2. The longitudinal helicity amplitude S 1/2, which was previously found from CLAS ep -> ep π0,en π+ data to be large and positive at Q2 = 0.4,0.65 GeV2, drops with Q2. Available model predictions for gamma*p -> N(1440)P11 allow us to conclude that these results provide strong evidence in favor of N (1440) P11 as a first radial excitation of the 3q ground state. The results of the present paper also confirm the conclusion of our previous analysis for Q2< 1 GeV2 that the presentation of N(1440)P11 as a q3G hybrid state is ruled out.


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Original Publication Citation

Collaboration, C., Aznauryan, I. G., Burkert, V. D., Kim, W., Park, K., Adams, G., . . . Zhao, Z. W. (2008). Electroexcitation of the Roper resonance for 1.7 < Q² < 4.5GeV² in ep → enπ+. Physical Review C, 78(4), 045209. doi:10.1103/PhysRevC.78.045209


0000-0003-1582-2376 (Dodge), 0000-0001-7282-8120 (Hyde), 0000-0003-2243-6836 (Kuhn), 0000-0001-5416-2900 (Weinstein)