Physics – Nuclear Physics – Nuclear Experiment
Scientific paper
2008-04-03
Phys.Rev.C78:045209,2008
Physics
Nuclear Physics
Nuclear Experiment
6 pages, 2 figures
Scientific paper
10.1103/PhysRevC.78.045209
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 pi+ 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 results. It is found that the transverse helicity amplitude A_{1/2} for the gamma* p -> N(1440)P11 transition, which is large and negative at Q2=0, becomes large and positive at Q2 ~ 2 GeV2, and then drops slowly with Q2. The longitudinal helicity amplitude S_{1/2}, which was previously found from CLAS ep -> eppi0,enpi+ 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 3qG hybrid state is ruled out.
Aznauryan Inna G.
Burkert Volker D.
collaboration The CLAS
Kim Woongnae
Park Kyungwha
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