Deep Inelastic Scattering From Heavy Nuclei and Medium Modifications of Nucleon Properties

G.A. Miller and J.R. Smith (graduate student)

The experience gained in working with light-front techniques [51] has given us the technical tools and the physics insight to allow us to develop improved approaches to reproducing the existing data and to hope to predict the existence of new phenomena. Our first result is that that conventional low energy nuclear physics with structureless hadrons provides an insufficient mechanism for producing the EMC effect [52,53]. Therefore we aim to see how the structure of a nucleon is modified by the effects of the medium. To do this we need to use a reasonable model of the nucleon. With the success of the Chiral Quark-Soliton Model ($\chi$QSM)[54] in calculating a wide class of nucleon observables using very few parameters (which can actually be directly calculated in the ILM thereby establishing a close link with QCD), we have implemented a program to apply the model to nuclear structure so that the composite nature of the nucleon is taken into account. We can not only fit the relatively macroscopic bulk nuclear properties (binding and saturation), but also calculate the relatively microscopic modification of quark and antiquark distributions (for which the $\chi$QSM has particularly desirable theoretical properties such as positivity) in nuclear matter. Our preliminary results are that these distributions (evolved to $Q^2= 200 {\rm GeV}^2$) provide a quantitative explanation of the EMC effect consistent with Drell-Yan experiments within the expected accuracy of the model. Besides this specific example, the program provides fertile theoretical ground to calculate medium modifications for a wide class of observables. This experience has given us the technical tools and physical insight to allow us to develop improved approaches to reproducing existing data and to hope to predict the existence of new phenomena. The extraction of solid conclusions about medium modifications from the data is a difficult problem, but informal discussions with several different experimentalists at recent meetings indicate the existence of considerable interest in making experiments with improved accuracy.