JLab Measurements of the ${}^3\mathrm{He}$ Form Factors at Large Momentum Transfers

The charge and magnetic form factors, $F_C$ and $F_M$, respectively, of ${}^3\mathrm{He}$ are extracted in the kinematic range $25{\mathrm{fm}}^{-2}\le Q^2\le 61{\mathrm{fm}}^{-2}$ from elastic electron scattering by detecting ${}^3\mathrm{He}$ recoil nuclei and scattered electrons in coincidence with the two High Resolution Spectrometers of the Hall A Facility at Jefferson Lab. The measurements find evidence for the existence of a second diffraction minimum for the magnetic form factor at $Q^2=49.3{\mathrm{fm}}^{-2}$ and for the charge form factor at $Q^2=62.0{\mathrm{fm}}^{-2}$. Both minima are predicted to exist in the $Q^2$ range accessible by this Jefferson Lab experiment. The data are in qualitative agreement with theoretical calculations based on realistic interactions and accurate methods to solve the three-body nuclear problem.

Figure 1

${}^3\mathrm{He}$ elastic structure function $A(Q^2)$ data from this experiment, compared to selected previous data and the present theoretical calculation using the hyperspherical harmonics variational method (see the text).

Figure 2

Absolute values of the ${}^3\mathrm{He}$ charge form factor $F_C$, as determined from this experiment. Also shown are selected previous data and the present theoretical calculation using the hyperspherical harmonics variational method (see the text).

Figure 3

Absolute values of the ${}^3\mathrm{He}$ magnetic form factor $F_M$, as determined from this experiment. Also shown are selected previous data and the present theoretical calculation using the hyperspherical harmonics variational method (see the text).

Figure 4

Algebraic values of the ${}^3\mathrm{He}$ charge and magnetic form factors over a selected $Q^2$ range. Also shown are algebraic values of the ${}^4\mathrm{He}$ charge form factor over the same $Q^2$ range [21]. The dashed lines have been drawn to just guide the eye through the data.