Spin dipole and quadrupole resonances in 40Ca.

Abstract

Angular distributions of the double differential cross section ${d}^{2}$\ensuremath{\sigma}/d\ensuremath{\Omega} dE(\ensuremath{\sigma}) and the spin-flip probability ${S}_{\mathrm{nn}}$ have been measured for inclusive proton inelastic scattering from $^{40}\mathrm{Ca}$ at 319 MeV. Excitation energies (\ensuremath{\omega}) up to about 40 MeV have been investigated over the angular range from 3.5\ifmmode^\circ\else\textdegree\fi{} to 12\ifmmode^\circ\else\textdegree\fi{} in the laboratory (0.3 to 0.9 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$). Here, multipole decompositions of angular distributions of \ensuremath{\sigma}${S}_{\mathrm{nn}}$ for the $^{40}\mathrm{Ca}$(p\ensuremath{\rightarrow},p\ensuremath{\rightarrow} ') reaction at 319 MeV have been performed in order to compare \ensuremath{\Delta}S=1 strength observed with sum rules. In contrast to the well-known quenching of Gamow-Teller and M1 resonances, the spin-dipole resonance has a total measured strength which is larger than that predicted by the energy-weighted sum rule. The spin-dipole strength distribution supports asymmetric widths predicted by calculations including 2p-2h mixing. The spin-quadrupole resonance is observed near \ensuremath{\omega}=35 MeV and its total strength for \ensuremath{\omega}<40 MeV estimated.