Pion inelastic scattering to the low-lying excited states ofLi6

Abstract

The excitation function for ${\ensuremath{\pi}}^{+}$ inelastic scattering to the ${0}^{+}$, $T=1$, 3.563-MeV level of $^{6}\mathrm{Li}$ has been measured at a constant momentum transfer $q\ensuremath{\simeq}109$ MeV/c for incident pion energies from 100 to 260 MeV. Although the differential cross sections extracted for the natural-parity transitions to the ${3}^{+}$, $T=0$, 2.185-MeV and ${2}^{+}$, $T=0$, 4.25-MeV levels are well reproduced within the framework of the distorted-wave impulse approximation, distorted-wave impulse approximation calculations fail to reproduce the anomalous excitation function observed for the transition to the 3.563-MeV level. The shape of the 3.563-MeV excitation function is similar to that previously observed for ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$ inelastic scattering to the ${1}^{+}$, $T=1$, 15.11-MeV state of $^{12}\mathrm{C}$ [C. L. Morris et al., Phys. Lett. 108B, 172 (1982)]. The same mechanism may be responsible for the observed excitation functions of both $\ensuremath{\Delta}S=\ensuremath{\Delta}T=1$ transitions. A possible mechanism is the previously proposed direct excitation of $\ensuremath{\Delta}$-particle-nucleon-hole ($\ensuremath{\Delta}\ensuremath{-}h$) components in the wave functions.