Return of the EMC effect: Finite nuclei

Abstract

A light front formalism for deep inelastic lepton scattering from finite nuclei is developed. In particular, the nucleon plus momentum distribution and a finite system analog of the Hugenholtzvan Hove theorem are presented. Using a relativistic mean field model, numerical results for the plus momentum distribution and ratio of bound to free nucleon structure functions for Oxygen, Calcium and Lead are given. We show that we can incorporate light front physics with excellent accuracy while using easily computed equal time wavefunctions. Assuming nucleon structure is not modified in-medium we find that the calculations are not consistent with the binding effect apparent in the data not only in the magnitude of the effect, but in the dependence on the number of nucleons.

Low-Qscaling, duality, and the EMC effect

“…[28] predict that the high-ξ crossover point in carbon occurs at lower ξ than in heavier nuclei, as was observed in the data. However, they predict a crossover at much larger ξ for 4 He. Similarly, Ref.…”

“…More detailed calculations have been done to determine the effect of binding and Fermi motion, but except for calculations of 3,4 He, most of these calculations were performed for a Fermi gas model or for infinite nuclear matter, with the density varied to approximate the finite nuclei. These calculations do not show any significant change in the ξ dependence for heavy (A > 10) nuclei.…”

“…If the nuclear structure function in this region is expressed as a convolution of proton and neutron structure functions, there are two alternative approaches used to describe the observed medium effect: (1) incorporating nuclear physics effects that modify the energy-momentum behavior of the bound proton with respect to the free proton, or (2) incorporating changes to the internal structure of the bound proton. It has been argued, most recently in [4], that the binding of nucleons alone can not explain the EMC effect. In addition, several attempts to explain the EMC effect in terms of explicit mesonic components appear to be ruled out due to limits set by Drell-Yan measurements [5].…”

Hard QCD Processes in the Nuclear Medium

“…3.5b is evaluated. The effective Feynman rules give 65) where the momenta are as depicted in Fig. 3.5b.…”

“…Additionally, several theoretical works by Miller and Smith [64,65] rigorously demonstrate that the dip in R EMC in the region 0.35 ≤ x ≤ 0.7 cannot be accounted for by nucleonic motion alone, meaning that modifications of the quark and gluon degrees of freedom of the bound nucleons do indeed need to be accounted for.…”