Pion scattering to 4(-) states in 14C.

Abstract

Angular distributions and excitation functions for inelastic scattering of ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ from $^{14}\mathrm{C}$ were measured at incident pion energies near the ${\ensuremath{\Delta}}_{33}$ resonance. Three states at excitation energies 11.7, 15.2, and 17.3 MeV were identified as ${4}^{\mathrm{\ensuremath{-}}}$ states. Isovector and isoscalar spectroscopic amplitudes ${Z}_{0}$ and ${Z}_{1}$, and equivalently, neutron and proton amplitudes ${Z}_{\mathrm{n}}$ and ${Z}_{\mathrm{p}}$ were deduced by comparison with microscopic distorted wave impulse approximation calculations. The 11.7-MeV state was found to be excited with a ${Z}_{\mathrm{n}/{Z}_{\mathrm{p}}}$ amplitude ratio of -1/3, resulting in a complete cancellation of the ${\ensuremath{\pi}}^{+}$ cross section. A nearly pure proton excitation was observed for the transition to the 17.3-MeV state. Both results are in qualitative agreement with the presented shell-model calculations. A poor correspondence with theory is found for the 15.2-MeV state. Data and distorted-wave impulse approximation calculations using shell-model wave functions are presented for the first ${3}^{\mathrm{\ensuremath{-}}}$ state at 6.73 MeV as an example of a transition dominated by \ensuremath{\Delta}S=0 (no spin transfer). Its excitation function and angular-distribution shape contrast sharply with the transitions to the ${4}^{\mathrm{\ensuremath{-}}}$ states that proceed by \ensuremath{\Delta}S=1.