Particle-hole strength excited in theCa40(p,n)40Sc reaction at 134 MeV

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Abstract

The $^{40}\mathrm{Ca}$(p,n${)}^{40}$Sc reaction was studied at 134 MeV. Neutron energy spectra were measured by the time-of-flight technique with resolutions of 220 keV at angles from 0\ifmmode^\circ\else\textdegree\fi{} to 41\ifmmode^\circ\else\textdegree\fi{} and 415 keV out to 62\ifmmode^\circ\else\textdegree\fi{}. The ${2}^{\mathrm{\ensuremath{-}}}$,${3}^{\mathrm{\ensuremath{-}}}$,${4}^{\mathrm{\ensuremath{-}}}$,${5}^{\mathrm{\ensuremath{-}}}$ band of states based on the (${f}_{7/2}$,${d}_{3/2}^{\mathrm{\ensuremath{-}}1}$) 1p1h structure was observed at low excitation energies, in good agreement with known analog states in $^{40}\mathrm{Ca}$ and $^{40}\mathrm{K}$. The shapes of the cross-section and analyzing-power angular distributions are in good agreement with distorted-wave impulse-approximation calculations using simple 1p1h (Tamm-Dancoff approximation) shell-model wave functions. A relatively strong transition to a state at ${E}_{x}$=2.3 MeV with L=3 is identified tentatively as a ${4}^{\mathrm{\ensuremath{-}}}$ state with the predominant 1p1h structure (1${f}_{7/2}$,2${s}_{1/2}^{\mathrm{\ensuremath{-}}1}$).The excitation of the (T=1) ${6}^{\mathrm{\ensuremath{-}}}$ (${f}_{7/2}$,${d}_{5/2}^{\mathrm{\ensuremath{-}}1}$) stretched state is observed near ${E}_{x}$=7 MeV, fragmented over approximately 3 MeV. The normalization factor required to make a distorted-wave impulse-approximation calculation agree in magnitude with the ${6}^{\mathrm{\ensuremath{-}}}$ excitation is 0.35, which is larger than the normalization factor for this excitation in mass 28, analyzed in a similar manner. The L=1 giant resonance is observed to be centered near ${E}_{x}$=10 MeV with a width (full width at half maximum) of about 5 MeV, and a distorted-wave impulse-approximation normalization factor of 0.16. Two ${1}^{+}$ excitations are observed at ${E}_{x}$=2.7 and 4.3 MeV which indicate directly the presence of ground-state correlations in the $^{40}\mathrm{Ca}$ target. The fact that the analog of the higher ${1}^{+}$ excitation is not seen in inelastic electron scattering indicates strong interference between spin and orbital current contributions. The effect of ground-state correlations on the 1p1h wave functions was investigated by performing calculations which allowed multiparticle-multihole correlations in the ${d}_{3/2}$ and ${f}_{7/2}$ orbitals. The distorted-wave impulse-approximation normalization factors obtained with these wave functions were found to increase by a factor of about 2 relative to those obtained with $^{40}\mathrm{Ca}$ assumed to be a closed core.

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