Effect of the tensor force on gamma-ray de-excitation angular distributions from dipole states populated in theC12(p,p′) reaction

Abstract

Angular distributions have been measured for the de-excitation gamma rays from the isoscalar and isovector ${1}^{+}$ states populated in the $^{12}\mathrm{C}$($p$,${p}^{\ensuremath{'}}$) reaction at ${E}_{p}(\mathrm{lab})=22\ensuremath{-}27$ MeV. Fluctuations in the ${A}_{0}$ coefficients, which measure the total excitation cross sections, are observed to decrease with energy toward the high end of the region investigated. The ${a}_{2}$ coefficients are still fluctuating at 27 MeV, but exhibit reasonably well-defined average values of about -0.40 and 0.15 for the $T=0$ and $T=1$ levels, respectively. Microscopic distorted-wave calculations based on a realistic $G$ matrix interaction, while not sufficient to completely describe the present data, suggest that the isospin dependence of the ${a}_{2}$ coefficients is associated with the tensor force. The theoretical calculations have been extended to 50 MeV and this effect of the tensor force persists.NUCLEAR REACTIONS $^{12}\mathrm{C}$($p$,${p}^{\ensuremath{'}}\ensuremath{\gamma}$) ${E}_{p}=22\ensuremath{-}27$ MeV; measured gamma-ray angular distribution; $M1$ states miscroscopic DWBA analysis.