Analysis of Electron-He3Scattering

Measurements of elastic electron-${\mathrm{He}}^3$ scattering have shown that the magnetic form factor $F_M$ decreases less rapidly with $q^2$ than the electric form factor $F_E$ in the range $0\le q^2\le 5$ ${\mathrm{F}}^{-2\mathrm{}}$. We interpret the difference as due to the effect of the exchange magnetic moment of ${\mathrm{He}}^3$, which should have a spatial extension appreciably smaller than that of the probability density. Assuming that the static exchange moment is -0.27 nm, we determine the shape of the form factor $F_x$ of this moment from $F_M\left(q^2\right)$ and $F_E\left(q^2\right)$. $F_x\left(q^2\right)$ can be fitted with the expression $1-(0.1\pm 0.02)q^2$. Our model gives explicit predictions for the form factors in electron-${\mathrm{H}}^3$ scattering.