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  • Transition form factors: γ+...
    Lu, Y.; Chen, C.; Cui, Z. -F.; Roberts, C. D.; Schmidt, S. M.; Segovia, J.; Zong, H. -S.

    Physical review. D, 08/2019, Letnik: 100, Številka: 3
    Journal Article

    <div class="content" data-loaded="yes">We report that electroproduction form factors describing the γ*p → Δ + ( 1232 ) , Δ + ( 1600 ) transitions are computed using a fully dynamical diquark-quark approximation to the Poincaré-covariant three-body bound-state problem in relativistic quantum field theory. In this approach, the Δ ( 1600 ) is an analogue of the Roper resonance in the nucleon sector, appearing as the simplest radial excitation of the Δ ( 1232 ) . Precise measurements of the γ*p → Δ + ( 1232 ) transition already exist on 0≤Q2≲8 GeV2 , and the calculated results compare favorably with the data outside the meson-cloud domain. The predictions for the γ*p → Δ + ( 1600 ) magnetic dipole and electric quadrupole transition form factors are consistent with the empirical values at the real photon point, and extend to Q2≈6mp2 , enabling a meaningful direct comparison with experiment once analysis of existing data is completed. In both cases, the electric quadrupole form factor is particularly sensitive to deformation of the Δ -baryons. Interestingly, while the γ*p → Δ + ( 1232 ) transition form factors are larger in magnitude than those for γ*p → Δ + ( 1600 ) in some neighborhood of the real photon point, this ordering is reversed on Q2≳2mp2 , suggesting that the γ*p → Δ + ( 1600 ) transition is more localized in configuration space.