Observation of large missing-momentum (e,e′p) cross-section scaling and the onset of correlated-pair dominance in nuclei

We report the measurement of xB scaling in (e,e′p) cross-section ratios off nuclei relative to deuterium at large missing momentum of 350≤pmiss≤600 MeV/c. The observed scaling extends over a kinematic range of 0.7≤xB≤1.8, which is significantly wider than 1.4≤xB≤1.8 previously observed for inclusive (e,e′) cross-section ratios. The xB-integrated cross-section ratios become constant (i.e., scale) beginning at pmiss≈kF, the nuclear Fermi momentum. Comparing with theoretical calculations we find good agreement with generalized contact formalism calculations for high missing momentum (>375 MeV/c), suggesting the observed scaling results from interacting with nucleons in short-range correlated (SRC) pairs. For low missing momenta, mean-field calculations show good agreement with the data for pmiss<kF, and suggest a potential non-negligible contribution to the measured cross-section ratios from scattering off single, uncorrelated, nucleons up to pmiss≈350 MeV/c. Therefore, SRCs become dominant in nuclei at pmiss≈350 MeV/c, well above the nuclear Fermi Surface of kF≈250 MeV/c.