Electromagnetic properties of the Delta (1232)
Oct, 1996Citations per year
Abstract:
We calculate the electromagnetic moments and radii of the Delta(1232) in the nonrelativistic quark model, including two-body exchange currents. We show that two-body exchange currents lead to nonvanishing Delta and N-->Delta transition quadrupole moments even if the wave functions have no D-state admixture. The usual explanation based on the single-quark transition model involves D-state admixtures but no exchange currents. We derive a parameter- free relation between the N-->Delta transition quadrupole moment and the neutron charge radius: Q(N-->Delta) = r~2(neutron)/sqrt(2). Furthermore, we calculate the M1 and E2 amplitudes for the process photon + N -->Delta. We find that the E2 amplitude receives sizeable contributions from exchange currents. These are more important than the ones which result from D-state admixtures due to tensor forces between quarks if a reasonable quark core radius of about 0.6 fm is used. We obtain a ratio of E2/M1=-3.5%.Note:
- 32 pages, LaTeX, 6 Postscript figures, to appear in Physical Review C
- Delta(1232): form factor
- Delta(1232): electric moment
- Delta(1232): magnetic moment
- quark: nonrelativistic
- current: exchange
- exchange: two-particle
- form factor: transition
- photon nucleon: exclusive reaction
- Delta(1232): photoproduction
- helicity: amplitude analysis
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