JLab Measurement of the ${}^4$He Charge Form Factor at Large Momentum Transfers

The charge form factor of ^4He has been extracted in the range 29 fm${}^{-2}$ $\le Q^2\le 77$ fm${}^{-2}$ from elastic electron scattering, detecting ${}^4$He nuclei and electrons in coincidence with the High Resolution Spectrometers of the Hall A Facility of Jefferson Lab. The results are in qualitative agreement with realistic meson-nucleon theoretical calculations. The data have uncovered a second diffraction minimum, which was predicted in the $Q^2$ range of this experiment, and rule out conclusively long-standing predictions of dimensional scaling of high-energy amplitudes using quark counting.