Quadrupole Transition in the Constituent Quark Model

Information on the intrinsic deformation of the proton can be obtained by studying the electromagnetic p → ∆+ quadrupole transition. Recent experiments have shown that the electric quadrupole (E2) strength in γp → ∆+ is about 10 times larger than predicted by the simple quark model using only one-body currents. Our analysis provides evidence for the dominance of exchange currents in the N → ∆ quadrupole transition, and identifies the physical mechanism leading to the observed E2 strength.