Moments of the Neutron Charge Form Factor and theN→ΔQuadrupole Transition

Recent data allow a new parametrization of the neutron charge form factor $G_E^n$. A parameter-free quark-model relation between $G_E^n$ and the $N\to \Delta$ quadrupole form factor $G_{C2\mathrm{}}^{N\to \Delta }$ is used to predict $G_{C2\mathrm{}}^{N\to \Delta }$ from $G_E^n$ data. In particular, $〈r_n^2〉$ is related to $N\to \Delta$ quadrupole moment $Q_{N\to \Delta }$, while $〈r_n^4〉$ connects to the $N\to \Delta$ quadrupole transition radius $〈r_{N\to \Delta }^2〉$. From the latter we derive an experimental value for the charge radius of the light constituent quarks $r_{\gamma q}=0.8\mathrm{}\mathrm{fm}$. Finally, the $C2\mathrm{}/M1\mathrm{}$ ratio in pion electroproduction is predicted from the elastic neutron form factor data.