Observation of nuclear scaling in theA(e,e′)reaction atxB

Abstract

The ratios of inclusive electron scattering cross sections of 4 He, 12 C, and 56 Fe to 3 He have been measured for the first time. It is shown that these ratios are independent of x B at Q 2 Ͼ1.4 GeV 2 for x B Ͼ1.5, 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 Q 2 Ͼ1.4 GeV 2 and x B Ͼ1.5 is consistent with the kinematical expectation that two-nucleon short range correlations ͑SRC͒ dominate the nuclear wave function at p m տ300 MeV/c. The values of these ratios in the scaling region can be related to the relative probabilities of SRC in nuclei with Aу3. Our data, combined with calculations and other measurements of the 3 He/deuterium ratio, demonstrate that for nuclei with Aу12 these probabilities are 4.9-5.9 times larger than in deuterium, while for 4 He it is larger by a factor of about 3.8.

Final-state interactions in two-nucleon knockout reactions

“…A lot of information regarding nuclear SRC has been obtained by measuring cross-section rations over extended ranges of the phase space [4,5,21,25,27].…”

“…The short-and medium-range components of the nucleon-nucleon interaction induce beyond mean-field high-momentum and highdensity fluctuations in the nuclear medium, thereby giving rise to fat tails in the nuclear momentum distributions [1][2][3]. The magnitude of nuclear SRC has been linked to plateaus in ratios of cross sections of inclusive electron scattering off different nuclei [4][5][6], and to the size of the EMC effect [7].…”

Hard QCD Processes in the Nuclear Medium

“…Universality of the 3N SRC part of the LCFD entails [8,[34][35][36]. These are compared to the a 3 (A) values reported by CLAS [8].…”

“…This essentially describes how nucleons of "flavor" N = p and N = n are distributed over various values of the (scaled) light cone momentum fraction 35) as well as the nucleon transverse momentum p ⊥ . The LCFD is defined in analogy to the parton distribution function, but instead it describes the distribution of nucleons inside a nucleus.…”

“…When accounting for two-nucleon SRCs, the values a 2 ( 56 Fe) = 5.58 (from [8,35]) and a 2 ( 208 Pb) = 5.6 (a conservative estimate) are used to characterize their strengths. When two-nucleon SRCs are accounted for, in order that the LCFD for the proton and neutron be respectively normalized to Z and (A − Z), the mean field contribution must be diluted by a factor of a …”