The E2/M1 Mixing Ratio in the Excitation of the Δ from Polarized Photo-Reactions
In constituent quark models, a tensor interaction, mixing quark spins with their relative motion, is introduced to reproduce the observed baryon spectrum. This has a consequence completely analogous to the nuclear tensor force between the n and p in deuterium. A D state component is mixed into what would otherwise be a purely S-wave object. The D-wave component breaks spherical symmetry, resulting in a non-vanishing <r2Y2> matrix element for the nucleon and a static quadrupole moment and deformation for its first excited state, the Δ resonance, at ∽325 MeV. The magnitude and sign of this D-state component are quite sensitive to the internal structure of the proton and have been of great interest in recent years .
KeywordsCompton Scattering Cross Section Ratio Tensor Interaction National Synchrotron Light Source Unpolarized Cross Section
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