Analyzing powers for proton inelastic scattering to unnatural-parity states inCa40andSi28

Abstract

Cross sections and analyzing powers in proton inelastic scattering leading to unnatural parity states of ${2}^{\ensuremath{-}}$, $T=0$ (6.025 and 6.75 MeV), ${2}^{\ensuremath{-}}$, $T=1$ (8.42 MeV) in $^{40}\mathrm{Ca}$ and ${6}^{\ensuremath{-}}$, $T=0$ (11.58 MeV) and ${6}^{\ensuremath{-}}$, $T=1$ (14.36 MeV) in $^{28}\mathrm{Si}$ were measured at 65 MeV. These states are pair states of different isospin with the same spin and parity. The analyzing powers for a pair of $T=0$ and $T=1$ excitations in $^{40}\mathrm{Ca}$ show an isospin dependence not observed in $^{28}\mathrm{Si}$. The measured angular distributions were compared with microscopic distorted-wave Born approximation calculations using two versions of the effective nucleon-nucleon interaction. As expected, the interaction emphasizing the tensor contribution predicts analyzing powers and cross sections in better agreement with the experimental data. As factors to produce a difference in the analyzing powers between the $T=0$ and the $T=1$ states, the effect of two transferred orbital angular momentum amplitudes allowed in a transition and the energy dependence of the isoscalar spin-dependent terms in the effective interaction are discussed.NUCLEAR REACTIONS $^{40}\mathrm{Ca}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}, {p}^{\ensuremath{'}})^{40}\mathrm{Ca}$, $^{28}\mathrm{Si}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}, {p}^{\ensuremath{'}})^{28}\mathrm{Si}$, $^{24}\mathrm{Mg}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}, {p}^{\ensuremath{'}})^{24}\mathrm{Mg}$, $E=65$ MeV, unnatural parity states of ${E}_{x}=6\ensuremath{-}15$ MeV, measured $\ensuremath{\sigma}(\ensuremath{\theta})$, analyzing power ${A}_{y}(\ensuremath{\theta})$, resolution \ensuremath{\sim}35 keV, DWBA analysis.