l - th / 9 61 00 40 v 1 2 5 O ct 1 99 6 Electromagnetic Properties of the ∆ ( 1232 )
نویسنده
چکیده
We calculate the electromagnetic moments and radii of the ∆(1232) in the nonrelativistic quark model, including two-body exchange currents. We show that two-body exchange currents lead to nonvanishing ∆ and N → ∆ 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 → ∆ transition quadrupole moment and the neutron charge radius, namely QN→∆ = 1 √ 2 r2 n. Furthermore, we calculate the M1 and E2 amplitudes for the process γ + N → ∆. 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%.
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