Observation of nuclear scaling in the A(e,e′) reaction at xB>1

The ratios of inclusive electron scattering cross sections of 4He, 12C, and 56Fe to 3He have been measured for the first time. It is shown that these ratios are independent of xB at Q2>1.4GeV2 for xB>1.5, where the inclusive cross section depends primarily on the high momentum components of the nuclear wave function. The observed scaling shows that the momentum distributions at high-momenta have the same shape for all nuclei and differ only by a scale factor. The observed onset of the scaling at Q2>1.4GeV2 and xB>1.5 is consistent with the kinematical expectation that two-nucleon short range correlations (SRC) dominate the nuclear wave function at pm≳300MeV/c. The values of these ratios in the scaling region can be related to the relative probabilities of SRC in nuclei with A>~3. Our data, combined with calculations and other measurements of the 3He/deuterium ratio, demonstrate that for nuclei with A>~12 these probabilities are 4.9–5.9 times larger than in deuterium, while for 4He it is larger by a factor of about 3.8.