Measurements of ep → e'π+n at 1.6 < W <2.0 GeV and extraction of nucleon resonance electrocouplings at CLAS

Authors

The CLAS Collaboration
K. Park, Old Dominion University
K. P. Adhikari, Old Dominion University
M. J. Amaryan, Old Dominion University
L. El Fassi, Old Dominion University
Y. Prok, Old Dominion University
L. B. Weinstein, Old Dominion University

Document Type

Article

Publication Date

2015

DOI

10.1103/PhysRevC.91.045203

Publication Title

Physical Review C

Volume

91

Issue

4

Pages

045203

Abstract

Differential cross sections of the exclusive process ep -> e 'π⁺n were measured with good precision in the range of the photon virtuality Q² = 1.8-4.5 GeV² and the invariant mass range of the π⁺n final state W = 1.6-2.0 GeV using the Continuous Electron Beam Accelerator Facility Large Acceptance Spectrometer. Data were collected with nearly complete coverage in the azimuthal and polar angles of the n π⁺center-of-mass system. More than 37 000 cross-section points were measured. The contributions of the isospin I = ½ resonances N(1675) 5/2^-, N(1680) 5/2⁺, and N(1710) 1/2⁺ were extracted at different values of Q² using a single-channel, energy-dependent resonance amplitude analysis. Two different approaches, the unitary isobar model and the fixed-t dispersion relations, were employed in the analysis. We observe significant strength of the N(1675)5/2^- in the A(1/2) amplitude, which is in strong disagreement with quark models that predict both transverse amplitudes to be strongly suppressed. For the N(1680)5/2⁺ we observe a slow changeover from the dominance of the A_3/2 amplitude at the real photon point (Q² = 0) to a Q² where A_1/2 begins to dominate. The scalar amplitude S _1/2 drops rapidly with Q²consistent with quark model prediction. For the N(1710)½⁺ resonance our analysis shows significant strength for the A_½ amplitude at Q² < 2.5 GeV²_.

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Original Publication Citation

The CLAS Collaboration, Park, K., Aznauryan, I. G., Burkert, V. D., Adhikari, K. P., Amaryan, M. J., . . . Zonta, I. (2015). Measurements of ep → e'π+n at 1.6 < w <2.0 GeV and extraction of nucleon resonance electrocouplings at CLAS. Physical Review C, 91(4), 045203. doi:10.1103/PhysRevC.91.045203

Repository Citation

The CLAS Collaboration; Park, K.; Adhikari, K. P.; Amaryan, M. J.; Fassi, L. El; Prok, Y.; and Weinstein, L. B., "Measurements of ep → e'π+n at 1.6 < W <2.0 GeV and extraction of nucleon resonance electrocouplings at CLAS" (2015). Physics Faculty Publications. 221.
https://digitalcommons.odu.edu/physics_fac_pubs/221