Pionic interpretation of the EMC effect

The EMC effect: that the deep-inelastic electromagnetic structure functions of iron and deuterium are different: is readily interpreted in the framework of conventional hadronic physics. The effect arises mainly from the virtual pions in the nucleus. A simple model, in which the effect of the pions is described by a rescaled quark distribution, fits the EMC data with a pion enhancement of 12% per nucleon in iron. Results of detailed calculations of the pion distribution are presented which largely support this interpretation. A critical ingredient of the calculations is the influence of the nuclear medium on the pion propagation. The magnitude of the effect is consistent with the theory of the pion response function of nuclear matter, as presently known. Another essential part of the detailed theory is a correct treatment of momentum balance for the nucleons in the nucleus