Empirical deduction of a medium-modified chiral order parameter from 1s π- states in heavy nuclei

We propose a model-independent procedure to deduce empirically the isovector strength bi of the pion-nucleus interaction, which is related to possible modification of the pion-decay constant f(pi) and thus of the chiral order parameter, in the nuclear medium. The first procedure is to compare the Is binding energies of pi (-) in two nuclei which have different (N - Z)/A values. such as Pb-205 and Sn-115. The second, more direct way is to deduce b(1) from an observed isotope shift of the Is binding energy, such as in Sn-115 and Sn-123. (C) 2001 Elsevier Science BN. All rights reserved.