CLAS Physics Database

Measurement of ep→e′nπ+ at 1.6<W<2.0 GeV and extraction of nucleon resonance electrocoupling at CLAS

Spokespersons
K. Park, V.D. Burkert, I.G. Aznauryan
Year
2014
Abstract
The differential cross sections of exclusive process $ep \toe\pi^+n$ were measured in the range of the photon virtuality Q2 = 1.8-4.5GeV2, and the invariant mass range of the $\pi+n$ final state W = 1.6-2.0 GeV using the CEBAF Large Acceptance Spectrometer. Full angular distributions in azimuthal and polar angles were mapped out with good precision. More than 37,000 cross section points were measured. The contributions of the isospin I = 1/2 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. Differences resulting from these independent approaches are taken as model sensitivity of the analysis. We observe significant strength of the N(1675)5/2- in the A1/2 amplitude even at high Q2, in strong disagreement with quark models that predict both transverse amplitudes to be consistent with zero. For the N(1680)5/2+ we observe an unexpectedly slow changeover from the dominance of the A3/2 amplitude at the real photon point (Q2 = 0) to a Q2 where A1/2 begins to dominate, indicating significant strength from non-quark contribution even at large Q2. The scalar amplitude S1/2 drops rapidly with Q2 consistent with quark model prediction. For the N(1710)1/2+ resonance our analysis shows significant strength for the A1/2 amplitude at Q2 < 2.5GeV2.
Comment
polarization of electron beam : ~80%
Publication
  1. CLAS-Analysis Note 2014-105 arXiv:1412.0274
Quantities
dσ/dΩ

Measurements

ID Quantity Beam Target Final state Q2min,
GeV2
Q2max,
GeV2
Wmin,
GeV
Wmax,
GeV
E141M1 dσ/dΩ e p π+n 1.8 1.8 1.605 1.605
E141M2 dσ/dΩ e p π+n 1.8 1.8 1.615 1.615
E141M3 dσ/dΩ e p π+n 1.8 1.8 1.625 1.625
E141M4 dσ/dΩ e p π+n 1.8 1.8 1.635 1.635
E141M5 dσ/dΩ e p π+n 1.8 1.8 1.645 1.645
E141M6 dσ/dΩ e p π+n 1.8 1.8 1.655 1.655
E141M7 dσ/dΩ e p π+n 1.8 1.8 1.665 1.665
E141M8 dσ/dΩ e p π+n 1.8 1.8 1.675 1.675
E141M9 dσ/dΩ e p π+n 1.8 1.8 1.685 1.685
E141M10 dσ/dΩ e p π+n 1.8 1.8 1.695 1.695
E141M11 dσ/dΩ e p π+n 1.8 1.8 1.705 1.705
E141M12 dσ/dΩ e p π+n 1.8 1.8 1.715 1.715
E141M13 dσ/dΩ e p π+n 1.8 1.8 1.725 1.725
E141M14 dσ/dΩ e p π+n 1.8 1.8 1.735 1.735
E141M15 dσ/dΩ e p π+n 1.8 1.8 1.745 1.745
E141M16 dσ/dΩ e p π+n 1.8 1.8 1.755 1.755
E141M17 dσ/dΩ e p π+n 1.8 1.8 1.765 1.765
E141M18 dσ/dΩ e p π+n 1.8 1.8 1.775 1.775
E141M19 dσ/dΩ e p π+n 1.8 1.8 1.78 1.78
E141M20 dσ/dΩ e p π+n 1.8 1.8 1.83 1.83
E141M21 dσ/dΩ e p π+n 1.8 1.8 1.89 1.89
E141M22 dσ/dΩ e p π+n 1.8 1.8 1.95 1.95
E141M23 dσ/dΩ e p π+n 1.8 1.8 2.01 2.01
E141M24 dσ/dΩ e p π+n 2.2 2.2 1.605 1.605
E141M25 dσ/dΩ e p π+n 2.2 2.2 1.615 1.615
E141M26 dσ/dΩ e p π+n 2.2 2.2 1.625 1.625
E141M27 dσ/dΩ e p π+n 2.2 2.2 1.635 1.635
E141M28 dσ/dΩ e p π+n 2.2 2.2 1.645 1.645
E141M29 dσ/dΩ e p π+n 2.2 2.2 1.655 1.655
E141M30 dσ/dΩ e p π+n 2.2 2.2 1.665 1.665
E141M31 dσ/dΩ e p π+n 2.2 2.2 1.675 1.675
E141M32 dσ/dΩ e p π+n 2.2 2.2 1.685 1.685
E141M33 dσ/dΩ e p π+n 2.2 2.2 1.695 1.695
E141M34 dσ/dΩ e p π+n 2.2 2.2 1.705 1.705
E141M35 dσ/dΩ e p π+n 2.2 2.2 1.715 1.715
E141M36 dσ/dΩ e p π+n 2.2 2.2 1.725 1.725
E141M37 dσ/dΩ e p π+n 2.2 2.2 1.735 1.735
E141M38 dσ/dΩ e p π+n 2.2 2.2 1.745 1.745
E141M39 dσ/dΩ e p π+n 2.2 2.2 1.755 1.755
E141M40 dσ/dΩ e p π+n 2.2 2.2 1.765 1.765
E141M41 dσ/dΩ e p π+n 2.2 2.2 1.775 1.775
E141M42 dσ/dΩ e p π+n 2.2 2.2 1.78 1.78
E141M43 dσ/dΩ e p π+n 2.2 2.2 1.83 1.83
E141M44 dσ/dΩ e p π+n 2.2 2.2 1.89 1.89
E141M45 dσ/dΩ e p π+n 2.2 2.2 1.95 1.95
E141M46 dσ/dΩ e p π+n 2.2 2.2 2.01 2.01
E141M47 dσ/dΩ e p π+n 2.6 2.6 1.605 1.605
E141M48 dσ/dΩ e p π+n 2.6 2.6 1.615 1.615
E141M49 dσ/dΩ e p π+n 2.6 2.6 1.625 1.625
E141M50 dσ/dΩ e p π+n 2.6 2.6 1.635 1.635
E141M51 dσ/dΩ e p π+n 2.6 2.6 1.645 1.645
E141M52 dσ/dΩ e p π+n 2.6 2.6 1.655 1.655
E141M53 dσ/dΩ e p π+n 2.6 2.6 1.665 1.665
E141M54 dσ/dΩ e p π+n 2.6 2.6 1.675 1.675
E141M55 dσ/dΩ e p π+n 2.6 2.6 1.685 1.685
E141M56 dσ/dΩ e p π+n 2.6 2.6 1.695 1.695
E141M57 dσ/dΩ e p π+n 2.6 2.6 1.705 1.705
E141M58 dσ/dΩ e p π+n 2.6 2.6 1.715 1.715
E141M59 dσ/dΩ e p π+n 2.6 2.6 1.725 1.725
E141M60 dσ/dΩ e p π+n 2.6 2.6 1.735 1.735
E141M61 dσ/dΩ e p π+n 2.6 2.6 1.745 1.745
E141M62 dσ/dΩ e p π+n 2.6 2.6 1.755 1.755
E141M63 dσ/dΩ e p π+n 2.6 2.6 1.765 1.765
E141M64 dσ/dΩ e p π+n 2.6 2.6 1.775 1.775
E141M65 dσ/dΩ e p π+n 2.6 2.6 1.78 1.78
E141M66 dσ/dΩ e p π+n 2.6 2.6 1.83 1.83
E141M67 dσ/dΩ e p π+n 2.6 2.6 1.89 1.89
E141M68 dσ/dΩ e p π+n 2.6 2.6 1.95 1.95
E141M69 dσ/dΩ e p π+n 2.6 2.6 2.01 2.01
E141M70 dσ/dΩ e p π+n 3.15 3.15 1.605 1.605
E141M71 dσ/dΩ e p π+n 3.15 3.15 1.615 1.615
E141M72 dσ/dΩ e p π+n 3.15 3.15 1.625 1.625
E141M73 dσ/dΩ e p π+n 3.15 3.15 1.635 1.635
E141M74 dσ/dΩ e p π+n 3.15 3.15 1.645 1.645
E141M75 dσ/dΩ e p π+n 3.15 3.15 1.655 1.655
E141M76 dσ/dΩ e p π+n 3.15 3.15 1.665 1.665
E141M77 dσ/dΩ e p π+n 3.15 3.15 1.675 1.675
E141M78 dσ/dΩ e p π+n 3.15 3.15 1.685 1.685
E141M79 dσ/dΩ e p π+n 3.15 3.15 1.695 1.695
E141M80 dσ/dΩ e p π+n 3.15 3.15 1.705 1.705
E141M81 dσ/dΩ e p π+n 3.15 3.15 1.715 1.715
E141M82 dσ/dΩ e p π+n 3.15 3.15 1.725 1.725
E141M83 dσ/dΩ e p π+n 3.15 3.15 1.735 1.735
E141M84 dσ/dΩ e p π+n 3.15 3.15 1.745 1.745
E141M85 dσ/dΩ e p π+n 3.15 3.15 1.755 1.755
E141M86 dσ/dΩ e p π+n 3.15 3.15 1.765 1.765
E141M87 dσ/dΩ e p π+n 3.15 3.15 1.775 1.775
E141M88 dσ/dΩ e p π+n 3.15 3.15 1.78 1.78
E141M89 dσ/dΩ e p π+n 3.15 3.15 1.83 1.83
E141M90 dσ/dΩ e p π+n 3.15 3.15 1.89 1.89
E141M91 dσ/dΩ e p π+n 3.15 3.15 1.95 1.95
E141M92 dσ/dΩ e p π+n 3.15 3.15 2.01 2.01
E141M93 dσ/dΩ e p π+n 4.0 4.0 1.605 1.605
E141M94 dσ/dΩ e p π+n 4.0 4.0 1.615 1.615
E141M95 dσ/dΩ e p π+n 4.0 4.0 1.625 1.625
E141M96 dσ/dΩ e p π+n 4.0 4.0 1.635 1.635
E141M97 dσ/dΩ e p π+n 4.0 4.0 1.645 1.645
E141M98 dσ/dΩ e p π+n 4.0 4.0 1.655 1.655
E141M99 dσ/dΩ e p π+n 4.0 4.0 1.665 1.665
E141M100 dσ/dΩ e p π+n 4.0 4.0 1.675 1.675