Spin-Isospin Response in Nuclei
Recently it became available at Los Alamos (LAMPF) to polarize high energy proton beams and measure the polarization of outgoing protons in any direction. Using this facility, spin responses in nuclei were measured at E P = 500 MeV on Pb at the momentum transfer q = 1.75 fm-1, which corresponds to the momentum of large collectivity in pion channel . It was found that the ratios of the longitudinal spin response (σ • qe iqr ) against the transverse spin response (σ × qe iqr ) were close to 1; S L /S T ~1 . This finding was totally unexpected, since the effective interaction is attractive in the longitudinal channel, while it is repulsive in the transverse channel in the π + ϱ model . This result led the experimentalists to conclude that the pion field is not enhanced in nuclei . Hence, out of the quark and pion interpretations of the EMC effect, the latter was rejected.
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