Abstract

The helicity amplitudes of the electroexcitation of the Roper resonance are extracted for 1.7<Q2<4.5GeV2 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 γ *p→N(1440)P11 transition. It is found that the transverse helicity amplitude A1/2, which is large and negative at Q2=0, becomes large and positive at Q2 2GeV2, and then drops slowly with Q2. The longitudinal helicity amplitude S1/2, which was previously found from CLAS e→p→epπ0,enπ+ data to be large and positive at Q2=0.4,0.65GeV2, drops with Q2. Available model predictions for γ*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 qG3 hybrid state is ruled out. © 2008 The American Physical Society.