Inelastic proton scattering to particle-hole states inCa40and spin-isospin excitation of pion symmetry states

Abstract

Inelastic proton scattering to the ${(d\frac{3}{2})}^{\ensuremath{-}1}(f\frac{7}{2})$ particle-hole states in $^{40}\mathrm{Ca}$ were studied at the proton energy of 65 MeV by using a high resolution magnetic spectrograph. Angular distributions for both isoscalar mode ($T=0$) and isovector mode ($T=1$) excitations were reproduced by a distorted-wave Born approximation code with the microscopic particle-hole configurations. The effective interaction used consists of central, $\mathrm{LS}$, and tensor forces with Yukawa-type radial forms. The isovector spin excitation of the 8.424 MeV state (${J}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$, $T=1$) and the isoscalar spin excitation of the 6.751 MeV state (${J}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$, $T=0$) were compared to look for speculated precritical effects of pion condensation. The observed angular distributions for both the ${2}^{\ensuremath{-}}$, $T=1 \mathrm{and} {2}^{\ensuremath{-}}$, $T=0$ states are similar and smooth as a function of the momentum transfer $q$. No obvious enhancement around $q\ensuremath{\approx}2.5 {m}_{\ensuremath{\pi}}C$ due to the proximity of the pion condensation was found in the pion mode (${2}^{\ensuremath{-}}$, $T=1$) excitation. The observed feature is in accord with the smoothly $q$ dependent $\mathrm{LS}$ and tensor interactions.NUCLEAR REACTIONS $^{40}\mathrm{Ca}$($p$, ${p}^{\ensuremath{'}}$), $E=65$ MeV; measured $\ensuremath{\sigma}({E}_{{p}^{\ensuremath{'}}},\ensuremath{\theta})$, resolution \ensuremath{\sim} 15 keV, DWBA calculations, deduced nuclear effective interactions and nonexistence of pion opalescence enhancement.