Study of the pionic enhancement in O-16(p, p ')O-16(0(-) ,T=1) at 295 MeV

Abstract The cross section of the O 16 ( p , p ′ ) O 16 ( 0 − , T = 1 ) scattering was measured at a bombarding energy of 295 MeV in the momentum transfer range of 1.0 fm −1 ⩽ q c.m. ⩽ 2.1 fm −1 . The isovector 0 − state at E x = 12.8 MeV 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 q c.m. ≃ 1.7 fm −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.