PION EXCESS, NUCLEAR CORRELATIONS, AND THE INTERPRETATION OF ((P)OVER-RIGHT-ARROW,(N)OVER-RIGHT-ARROW) SPIN TRANSFER EXPERIMENTS

Conventional theories of nuclear interactions predict a net increase i n the distribution of virtual pions in nuclei relative to free nucleon s. Analysis of data from several nuclear experiments has led to claims of evidence against such a pion excess. These conclusions are usually based on a collective theory [random-phase approximation (RPA)] of th e pions, which may be inadequate. The issue is the energy dependence o f the nuclear response, which differs for theories with strong NN corr elations from the RPA predictions. In the present paper, information a bout the energy dependence is extracted from sum rules, which are calc ulated for such a correlated, noncollective nuclear theory. The result s lead to much reduced sensitivity of nuclear reactions to the correla tions that are responsible for the pion excess. The primary example is ((p) over right arrow,(n) over right arrow) spin transfer, for which the expected effects are found to be smaller than the experimental unc ertainties. The analysis has consequences for deep inelastic scatterin g experiments as well.