Electroexcitation of the Roper resonance for 1.7<Q{sup 2}<4.5 GeV{sup 2} in e-vectorp{yields}en{pi}{sup +}

• Published in: Physical review. C, Nuclear physics Vol. 78; no. 4
• Main Authors: Aznauryan, I. G., Yerevan Physics Institute, 375036 Yerevan, Burkert, V. D., Avakian, H., Carman, D. S., Cords, D., Degtyarenko, P. V., Deur, A., Elouadrhiri, L., Guo, L., Gyurjyan, V., Heddle, D., Ito, M. M., Mecking, B. A., Mestayer, M. D., Niczyporuk, B. B., Sharabian, Y. G., Smith, E. S., Stepanyan, S., Weygand, D. P., Wolin, E.
• Format: Journal Article
• Language: English
• Published: United States 15-10-2008
• Subjects: ACCURACY; AMPLITUDES; ASYMMETRY; CEBAF ACCELERATOR; CROSS SECTIONS; DISPERSION RELATIONS; ELECTRON-PROTON INTERACTIONS; ELECTROPRODUCTION; EXCITATION; FORECASTING; GEV RANGE 01-10; GROUND STATES; HELICITY; HYBRIDIZATION; ISOBAR MODEL; N-1440 BARYONS; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; PIONS PLUS; POLARIZED BEAMS; PROTONS
• ISSN: 0556-2813; 1089-490X
• DOI: 10.1103/PHYSREVC.78.045209

The helicity amplitudes of the electroexcitation of the Roper resonance are extracted for 1.7<Q{sup 2}<4.5 GeV{sup 2} from recent high precision JLab-CLAS cross section and longitudinally polarized beam asymmetry data for {pi}{sup +} 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 Q{sup 2} behavior of the helicity amplitudes for the {gamma}*p{yields}N(1440)P{sub 11} transition. It is found that the transverse helicity amplitude A{sub 1/2}, which is large and negative at Q{sup 2}=0, becomes large and positive at Q{sup 2}{approx_equal}2 GeV{sup 2}, and then drops slowly with Q{sup 2}. The longitudinal helicity amplitude S{sub 1/2}, which was previously found from CLAS e-vectorp{yields}ep{pi}{sup 0},en{pi}{sup +} data to be large and positive at Q{sup 2}=0.4,0.65 GeV{sup 2}, drops with Q{sup 2}. Available model predictions for {gamma}*p{yields}N(1440)P{sub 11} allow us to conclude that these results provide strong evidence in favor of N(1440)P{sub 11} 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 Q{sup 2}<1 GeV{sup 2} that the presentation of N(1440)P{sub 11} as a q{sup 3}G hybrid state is ruled out.