Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2011-12-09
Physics
High Energy Physics
High Energy Physics - Phenomenology
21 pages, 9 figures, 4 tables. Added references
Scientific paper
We study the N-Delta-gamma transition in the Dyson-Schwinger approach. The nucleon and Delta baryons are treated as quark-diquark bound states, where the ingredients of the electromagnetic transition current are computed self-consistently from the underlying dynamics in QCD. Although our approach does not include pion-cloud effects, we find that the electric and Coulomb quadrupole form-factor ratios R_EM and R_SM show good agreement with experimental data. This implies that the deformation from a spherical charge distribution inside both baryons can be traced back to the appearance of p waves in the nucleon and Delta bound-state amplitudes which are a consequence of Poincare covariance. On the other hand, the dominant transition amplitude, i.e. the magnetic dipole transition form factor, underestimates the data by ~25% in the static limit whereas agreement is achieved at larger momentum transfer, which is consistent with missing pion-cloud contributions. We furthermore find that the static properties of the form factors are not very sensitive to a variation of the current-quark mass.
Eichmann Gernot
Nicmorus Diana
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