Exchange Currents and Nucleon Deformation

Abstract

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