Study of the pionic enhancement in O16(p,p′)O16(0−,T=1) at 295 MeV

The cross section of the O16(p,p′)O16(0−,T=1) scattering was measured at a bombarding energy of 295 MeV in the momentum transfer range of 1.0fm−1⩽qc.m.⩽2.1fm−1. The isovector 0− state at Ex=12.8MeV is clearly separated from its neighboring states owing to the high energy resolution of about 30 keV. The cross section data were compared with distorted wave impulse approximation (DWIA) calculations employing shell-model wave functions. The observed cross sections around qc.m.≃1.7fm−1 are significantly larger than obtained by these calculations, suggesting pionic enhancement as a precursor of pion condensation in nuclei. The data are well reproduced by DWIA calculations using random phase approximation response functions including the Δ isobar that predict pionic enhancement.