Recoil polarization measurements for neutral pion electroproduction atQ2=1(GeV/c)2near t

Abstract

We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q 2 = 1.0 (GeV/c) 2 in 10 bins of 1.17 W 1.35 GeV across the resonance. A total of 16 independent response functions were extracted, of which 12 were observed for the first time. Comparisons with recent model calculations show that response functions governed by real parts of interference products are determined relatively well near the physical mass, W = M ≈ 1.232 GeV, but the variation among models is large for response functions governed by imaginary parts, and for both types of response functions, the variation increases rapidly with W > M . We performed a multipole analysis that adjusts suitable subsets of π 2 amplitudes with higher partial waves constrained by baseline models. This analysis provides both real and imaginary parts. The fitted multipole amplitudes are nearly model independent-there is very little sensitivity to the choice of baseline model or truncation scheme. (2007) models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe.

Jülich-Bonn-Washington Model for Pion Electroproduction Multipoles

“…It should be noted, however, that this study of experimental completeness assumed error-free measurements. In the Kelly paper [213], fits with different angular-momentum cutoffs were attempted, showing sensitivity to approximations made in their multipole analysis. duction websites [137,212] and codes allowed checks for consistency of conventions, definitions and naming schemes within the SAID database.…”

Measurement of the neutron charge radius and the role of its constituents

“…Finally, we perform the flavor decomposition of the neutron and the proton form factors measurements and derive the flavor dependent quark densities in the nucleon, which reveal with high precision the role of the quark contributions to the neutron charge radius. E /G n M : world data [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] (black open circles), ratios calculated from the N → ∆ measurements [24][25][26][27][28][29][30][31][32] through Eq. 1 for n b = 1 (filled-squares), and lattice Quantum Chromodynamics (LQCD) results (red open circles) 33 .…”

Nucleon resonance contributions to unpolarized inclusive electron scattering

“…The left column shows A 1/2 a nd the right column shows S 1/2 , while the central column shows A 3/2 when applicable. The data are from the RPP[56], CLAS[47-49, 51-53, 69] the E94014 experiment[62], MAMI[66], MIT/Bates[64], Hall A[63,65] and Hall C[67]. Electrocouplings of the N (1650) 1/2 − , N (1675) 5/2 − , N (1680) 5/2 + , ∆(1700) 3/2 − and N (1710) 1/2 + .…”