JLab APS Centennial Presentations | |||||
Photo-Production of the Delta with current quark masses Session NP01 - Poster Session IV. POSTER session, Tuesday evening, March 23 Exhibit Hall, GWCC George Strobel (Physics and Astronomy Dept., University of Georgia, Athens, Ga)
The proton and Delta are three quarks assumed solely in the
(1/2^+)^3 configuration, with angular momenta coupled
to 1/2 and 3/2 respectively. The three body Dirac equation
is solved with hypercentral linear and quadratic confining
potentials, including all 8 components of the composite
three quark wave function. With small quark masses, this
model reproduces the proton and delta energies, the proton
rms size, axial charge, and magnetic moment. The lower
components of the one quark wave function are (1/2^-).
These components have the orbital angular momentum needed
for the E2 photo-production amplitude not to vanish, and
contribute over 40 percent to the normalization. These are
neglected in constituent quark calculations. With all 8
component wave functions, the E2/M1 ratio is mostly given by
the first terms of -j_2(kr)/2j_1(kr)=-0.05. Assigning
anomalous magnetic moments to quarks, the proton magnetic
moment and the M1 photo-production amplitude can be
simultaneously reproduced with a quark mass of order 1 MeV.
About 20 percent of the M1 amplitude then comes from the
quark anomalous magnetic moment interaction.
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