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    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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