Differential cross sections and a complete set of polarization observables have been measured for quasielastic (p→,n→) reactions on 12C and 40Ca at a bombarding energy of 345 MeV. The laboratory momentum transfers are qlab ≃ 1.2, 1.7, and 2.0 fm-1 for 12C and qlab≃ 1.7 fm -1 for 40Ca. In these momentum transfer regions, the isovector spin-longitudinal interaction is attractive where the one-pion exchange is dominant. The spin-longitudinal and spin-transverse polarized cross sections, IDq and IDp, are deduced. The theoretically expected enhancement in the spin-longitudinal mode is observed at q lab≃1.7 and 2.0 fm-1. The observed IDq is consistent with the pionic enhanced IDq evaluated in distorted wave impulse approximation (DWIA) calculations employing random phase approximation (RPA) response functions. The enhanced IDq implies the existence of a precursor to pion condensation in nuclei. On the other hand, the theoretically predicted quenching in the spin-transverse mode is not observed. The observed IDp is not quenched, but rather enhanced relative to that predicted via the DWIA+RPA calculations. Two-step contributions are responsible in part for the enhancement of IDp.
ASJC Scopus subject areas
- Nuclear and High Energy Physics