The role of the pion cloud in electroproduction of the $Δ$(1232)

Abstract

We calculate the ratios $E2/M1$ and $C2/M1$ of the multipole amplitudes for electroproduction of the $Δ$(1232) in the range of photon virtuality $0<-K^2<1$~GeV$^2$ in a chiral chromodielectric model and a linear $σ$-model. We find that relatively large experimental values can be explained in terms of the pion contribution alone; the contribution arising from d-state quark admixture remains below 10\%. We describe the pion cloud as a coherent state and use spin and isospin projection to obtain the physical nucleon and the $Δ$. The $A_{1/2}$ and $A_{3/2}$ amplitudes are reasonably well reproduced in the $σ$-model; in the chromodielectric model, however, they are a factor of two too small.