Quark exchange in nuclei and the European Muon Collaboration effect.

Abstract

Quark exchange between nucleons bound in a nucleus can cause a shift in the momentum distribution of quarks relative to free nucleons. This is true even if nucleon properties, including size, remain unchanged in the nuclear environment. This shift in momentum leads to a contribution to the matrix elements of single-quark operators which is nonadditive, and therefore cannot be incorporated into a convolution model. For A=3 nuclei investigated here, such exchange contributions were found to be important, perhaps even dominant, in calculating the deviation from unity of the ratio of the nuclear structure function to that of the free nucleon (European Muon Collaboration ratio).