Return of the EMC effect

Abstract

The relationship between the properties of nuclear matter and structure functions measured in lepton-nucleus deep inelastic scattering is investigated using light front dynamics. We find that relativistic mean field models such as the Walecka, Zimanyi-Moszkowski (and point-coupling versions of the same) and Rusnak-Furnstahl models contain essentially no binding effect, in accord with an earlier calculation by Birse. These models are found to obey the Hugenholtz-van Hove theorem, which is applicable if nucleons are the only degrees of freedom. Any model in which the entire Fock space wave function can be represented in terms of free nucleons must obey this theorem, which implies that all of the plus momentum is carried by nucleons, and therefore that there will be essentially no binding effect. The explicit presence of nuclear mesons allows one to obtain a modified form of the Hugenholtz-van Hove theorem, which is equivalent to the often-used momentum sum rule. These results argue in favor of a conclusion that the depletion of the deep inelastic structure function observed in the valence quark regime is due to some interesting effect involving dynamics beyond the conventional nucleon-meson treatment of nuclear physics. miller/jasons/reorder.tex

Understanding the nucleon as a Borromean bound-state

“…These remarks concerning Faddeev wave function components with quark-diquark orbital angular momentum L 0 in the nucleon rest frame are consistent with the relativistic constituent-quark model study of Ref. [86] and the analysis of nucleon spin structure in Ref. [87].…”

Final analysis of proton form factor ratio data atQ2=4.0, 4.8, and 5.6 GeV2

“…Frank et al [85] calculated G p E and G p M in the lightfront CQM using the light-front nucleon wave function of Schlumpf [86], and predicted that G p E might change sign near 5.6 GeV 2 , a behavior inconsistent with current data, though qualitatively correct. In this model, constructing a Poincaré-invariant nucleon wavefunction that is also an eigenstate of spin leads to the substantial violation of hadron helicity conservation [87] responsible for the observed scaling of QF 2 /F 1 in the Q 2 range of present experiments. This feature is a consequence of the unitary Melosh rotation [88] which mixes quark spin states in the process of boosting the nucleon spin-flavor wavefunction from the rest frame to the light front.…”

The structure of the nucleon: Elastic electromagnetic form factors

“…French, Jennings, and Miller [223,224] focused on the effects of the nuclear medium upon the form factors, but also calculated the form factors of single free nucleons. They followed the work of Schumpf [221,222] and similarly found a decreasing G Ep /G Mp ratio, obtaining a zero between 5 and 6 GeV 2 for Q 2 .…”

“…Miller extended the calculation to larger Q 2 using a light-front version of the cloudy bag model calculation [128]. Starting from constituent quarks [224], using the Schlumpf wave function instead of bag wave functions for the quark core, Miller calculated the effects of the pion cloud through one-loop diagrams. The model gives a relatively good overall account of the form factor data at both lower Q 2 and higher Q 2 .…”